iMac 2019 slow after Sequoia 15.3.1 update

guido_no wrote:

The upgrade DIMMs are the same speed (266 MHz) as the original Apple ones.

There is much more to memory compatibility than just the memory speed (aka frequency). There are lots of other timings that must be met, but those details are not provided by Apple so it is critical that the memory vendor has guaranteed compatibility with your specific Mac. It has not been possible to purchase memory based just on speed & CL ratings since around 2005 before the Intel Core Duo CPUs were introduced (personal experience).

It doesn‘t matter if I take them out or take the original ones out. I tried all permutations, to no avail. The memory is installed according to Apple‘s specifications, but I will try to find more info.

Typically the Apple OEM memory is installed into the DIMM0 slots. New memory typically should be installed into the DIMM1 slots, but that is not always the case for all iMacs, but Apple's current documentation is not exactly clear on this point for some models (I read it two different ways).

What do you mean by ‚Logic Board‘? The main board? How is it related to the power supply? Are you saying that despite the extensive testing (several days) at the Apple Service Center there could still be undetected hardware failures?

Yes. I have seen lots of odd failures with the more recent Intel Macs. I've seen some Intel Macs run extremely slow. It used to be that it was easy to confirm by checking the CPU frequency since it would usually be throttled, but with later Intel Macs I have seen the CPU frequency be at 2.5 - 3.0 GHz, but the system has nothing but spinning wheels even with a clean install of macOS and no third party apps. I'm fortunate enough to have a good power supply for these iMacs so was able to confirm the issue was not the power supply, but the Logic Board itself. We had the Logic Board replaced and the iMac was working normally again.

Unfortunately the Apple Diagnostics rarely detect issues even when a hardware issue has been confirmed through other methods. It doesn't help that the current Apple diagnostics cannot be looped for hours since some failures require more time before a failure can be detected.

Many of Apple's techs may not have any real world generic computer troubleshooting experience. If the only training they have is based on Apple's training, then that training is very basic. It also doesn't help that they tend to only use Apple's own diagnostics instead of utilizing other diagnostic tools & resources. If the diagnostics don't reveal a problem and the tech cannot see the problem with a clean install of macOS, then they will say the computer is working fine. Apple doesn't even train their techs to read Kernel Panic reports for troubleshooting issues. Even an experienced repair tech will have problems troubleshooting these recent Macs since the least expensive and "easily" replaced components are the memory & power supply....the internal drives can be bypassed with an external boot drive.

I agree with not wanting to spend more money on this iMac, but it does really work very well (as long as there are no MacOS updates which mess things up).

If that is the only time you have issues, then I would suspect the drive itself, or perhaps the SATA Controller on the Logic Board (or the internal cables).

As a last resort I could attempt another clean install, but I hate to think that it will only last until the next (minor) update.

Since I've had to replace several Logic Boards on these 2019 & 2020 iMacs for similar types of issues, my money is on a defective Logic Board based on my own personal experiences. Unfortunately there probably is no way to confirm it.

I guess you could install macOS onto an external USB3 SSD to see how things go. You should be able to use the command line to download an older version of the macOS installer so that you could then test an OS update to see if the issue occurs with the external SSD. If the external SSD is fine, then it would point to an issue with the internal SSD, internal cable, or Logic Board especially if you can still reproduce the issue on the internal drive.

You can use the following Terminal commands to identify the available versions of macOS installers:

softwareupdate  --list-full-installers

Then use the following command to download a specific older installer so that you can install an update patch to test the system:

softwareupdate  -d  --fetch-full-installer  --full-installer-version  <macos-version>

You would replace "<macos-version>" with the version number for one of the items listed from the first command such as macOS 15.1.1 Sequoia....the command would be:

softwareupdate  -d  --fetch-full-installer  --full-installer-version  15.1.1

You would then create a bootable macOS USB installer using the instructions in the following Apple article:

Create a bootable installer for macOS - Apple Support

guido_no wrote:

But some extension might interfere with the proper operation of Sequoia.

Possible, but doubtful since the posted EtreCheck report did not really show anything worrisome to me (assuming you had issues with that installation of macOS where the report was made). I'm also not a macOS software expert, but can tell some of the worst offenders....plus I can identify items that I don't usually see in these reports...unusual can indicate a possible problem item.

Any idea how I might identify other potentially offending extensions?

Easiest way is to post the full EtreCheck report assuming the last one was only for a test installation.

If you want to easily test a clean install, then you can either create a new APFS volume on the internal Samsung SSD where you can install a fresh clean copy of macOS next to your existing installation (I'm assuming you have at least 80GB+ of Free space with that 2TB SSD). However, if the APFS file system or the internal Samsung SSD is the problem, then you will likely still experience the same issues.

Use more than one version of macOS on Mac - Apple Support

The best option in my opinion would be to install macOS onto an external USB3 SSD. Then boot from the external SSD to see how the system works. This should bypass any (or at least 99% of ) issues that may involve the internal Samsung SSD. Testing the system without installing any third part software and without restoring from a backup is best because if you have issues under those conditions, then you have proven you have a hardware issue of some sort.

From everything you have said here I believe you have a hardware issue of some sort. If it is not the memory or the Samsung SSD, then there really isn't anything else for you to do other than try moving the iMac to another location just in case you have some odd power issue with its current location (perhaps bad electrical outlet, or circuit, or some appliance that causes a power blip when it activates (AC, refrigerator, microwave, oven, laser printer, etc.). From my own personal experience I have no faith in those Logic Boards.....and some of your symptoms sound exactly like what I saw with a couple of my organization's 2017 - 2019 iMacs where Logic Boards were confirmed to be the issue since everything just worked after they were replaced.

FYI, if you can reproduce the issue with a clean install of macOS under the conditions I outlined, then a tech would know without a doubt you have a hardware issue of some sort. Except for the tech trying another power supply, everything else can be done by you with what I've laid out here in this thread.

guido_no wrote:

Any tips on finding the offending app? Anybody?

It is not so much an application or combination of applications.

Rather the External Samsung SSD 970 EVO 4 TB SSD drive 

The Write and Read speeds seem to be below normal for a SSD Drive  

Samsung SSD 970 EVO 4TB 4.00 TB (Solid State - TRIM: No)

Write speed: 493 MB/s

Read speed: 525 MB/s

https://semiconductor.samsung.com/consumer-storage/internal-ssd/970evo/#:~:text=Next%20level%20SSD%20speed,writes%20than%20the%20previous%20generation.

Hum and if I may inquire

The Apple Technician diagnosed a Fusion Drive issue and Apple Replaced it with the Samsung EVO SSD ?

That sounds weird to say the least

I could not confirm this as I have never had a machine serviced.let alone have the Drive replaced

Normally, Apple may replace Parts ( Fusion Drive ) will Apple Original Parts

As for why the Samsung EVO is not performing to expectations

I will request from one of My Go TO experts is hardware - Their Help

Almost all of the high CPU utilizations and crashes appear to all be related to the file system and Spotlight which is all about accessing the drive. Try running Disk Utility First Aid on the hidden Container. Within Disk Utility you may need to click "View" and select "Show All Devices" before the hidden Container appears on the left pane of Disk Utility. Even if the First Aid summary says everything is "Ok", click "Show Details" and scroll back through the report to see if any errors are shown. If there are errors, then run First Aid again until the errors are gone. If after several scans the errors still remain, then run First Aid from Recovery Mode. If after several scans from Recovery Mode the errors remain, then you will need to erase the whole physical SSD before reinstalling macOS.

I would also suggest enabling TRIM on the Samsung SSD by using the following command in the Terminal app:

sudo  trimforce  enable

This command will prompt for your admin password. Nothing will appear on the screen as you type the password, so press the "Return" key to submit the password.

Another possibility is the memory upgrade. What is the make & model of the memory upgrade? How long have you had this memory upgrade? Unfortunately Apple's documentation for proper installation of the memory is confusing. I'm not certain your memory is installed correctly even if the memory is compatible & healthy.

I have also seen odd issues with the 2019 iMac Logic Boards, so it would not surprise me if the Logic Board itself is bad. I have had a few of the 2019 & 2020 iMacs that had performance issues that were due to bad Logic Boards, but I was fortunate enough to have a spare power supply for testing purposes. Unfortunately there are no reliable tests. Also, make sure to disconnect all external devices in case one of them is causing a problem. I would even suggest using a wired keyboard & mouse to compare results.

FYI, I would not recommend spending any money on any of the Intel Macs especially the USB-C Intel Macs for multiple reasons.

Thank you for the additional information regarding who replaced the Original Fusion Drive

It was bugging me

I would also like to thank my colleague @HWTech for answering my request for help about your computers issue

Hardware is less so something in my toolbox of expertise

A quick search for TRIM

SSD TRIM helps improve the performance and longevity of SSD drives. Using the TRIM command reduces the amount of data an SSD needs to move during the garbage collection process and reduces the amount of erase cycles, enabling the drive to last longer.

guido_no wrote:

My iMac 2019,1 worked fine from early 2020 till end of 2024, right until the upgrade to Sequoia 15.1 (on Jan 2nd).

Did anything else change at that time? This includes any different connected devices or software changes?

Re-formatting and loading back my profile from Time Machine did not help.

Re-formatting and loading back only ‚data‘ (including ~/Library) from TM -> same issue.

Sounds like some setting could be the problem and it was brought back.

Re-formatting and clean install of Sequoia (15.3 by now) -> everything working perfectly!

Manually adding my data and apps -> still everything working fine.

Until (forced) update to Sequoia 15.3.1, last week -> same issue as after upgrade to Sequoia 15.1

Almost sounds like something was reinstalled or reconfigured that is causing the problem.

Of course, all of this may be coincidence. And I agree with you that the issue looks a lot like some spurious hardware issue.

A hardware issue could also cause all these issues as well. Sometimes it may take a little while for it to happen depending on the hardware issue & its severity. Some years ago I worked on a laptop where bad memory corrupted the file system, but it took about a week or so before the user started to notice problems after everything was re-imaged.

But, then again, if it is not coincidence, could some part of my data or settings (be it app, driver, setting, whatever…) be interfering with Sequoia? E.g. I just noticed that I have still an old driver for a Canon Lide300 scanner installed, which may not be compatible with Sequoia.

Welcome to my world. This is where testing with a clean install and a clean install on an external boot drive can help tremendously.

I keep the Apple DIMMs in their original slots, which must be 0 and 1 and add the update to slots 2 and 3. But even if I swap the Apple DIMMs with the update ones, the problem persists. So the issue is probably not related to the RAM.

The original Apple memory would have shipped installed into the DIMM0 slots which have an empty slot between them. I don't recall which physical slots are DIMM0, but they do alternate:

Bank A DIMM0

DIMM1

Bank B DIMM0

DIMM1

If you want to perform an extended memory test, you could create & use a bootable Memtest86 USB stick. Just make sure to only use the default Memtest86 settings since any modifications will cause the system to freeze.

Too bad the problem cannot be properly diagnosed. I would really need someone who can read the kernel panic logs. Do you know where I can find them, or where I can find more information about them?

The EtreCheck report you posted did not show any Kernel Panics. Most of the log summaries were showing high CPU utilization. If you do have any Kernel Panics, then those Kernel Panic logs would be located in "/Library/Logs/DiagnosticReports" with "kernel" and/or "panic" in the file name.

Rumours are being spread that Intel with their instructions that are wireless are ruining Intel chips, this is why, on Apple specific to make them look bad, I heard it from a programmer friend, it must be true