MacOS stutters every 2 seconds when an external monitor is plugged in

Question

Level 1

6 points

MacOS stutters every 2 seconds when an external monitor is plugged in

I’ve bought a new Macbook Pro 16”. There is stuttering right after I have my external monitor plugged in. Stuttering is observed on both displays (on internal Retina and on external LG Display) while having connected external LG display. Stuttering stops immediately right after ejecting the LG display.

There is two videos I’ve recorded to show this problem:

https://youtu.be/D5czg8gdKh4 – Stuttering when moving a window.
https://youtu.be/b4PGSEXCvMc – Stuttering when selecting a text.

My specs:

Notebook: Macbook Pro 16” 2019, 8-Core Intel Core i9, 16 GB RAM, 1TB SSD, Intel UHD Graphics 630, AMD Radeon Pro 5500M (4GB).

External Monitor: LG 29UM69G 29”.

OS Version: Catalina, 10.15.5 (19F101).

Periphery: Magic Keyboard 2, Magic Mouse 2, USB 2.0 no-name Mouse, original Apple USB-C to USB-C 0.8M cable (Apple Thunderbolt 3), HDMI to HDMI cable through original 3-in-1 adapter USB-C to [ USB-C, HDMI, USB 2.0 ].

What doesn’t help at all:

Installing the last update.
Connecting through USB-C-to-USB-C Thunderbolt 3 cable (instead of HDMI-to-HDMI plus HDMI-to-USB-C connector) – I’ve bought it just for solving this issue.
Resetting SMC and NVRAM.
Using another (new) user profile.
Closing the lid and working only with the external display.
Having both displays working but showing separate desktops.
Having both displays working with turned on displays mirroring.
Setting custom scaling (also tried choosing custom scaling by pressing Option key).
Using only the built-in trackpad.
Turning off bluetooth.
Removing mouse and trackpad plists from Libraries/Preferences folder.
Using no-name USB2.0 wired mouse.
The Diagnostic Tool (by pressing D) shows “No Issues Found”.
The Disk Utility Tool (by pressing Cmd + R) shows “No Issues Found”.

What helps (but these are not solutions):

Eject external display.
Using Bootcamp (this problem is not observed there at all).
Booting in Safe Mode (by pressing Shift after starting a computer).
Using my previous MacBook Pro 2015 15” (which also the last Catalina version) with the LG display.

Please, don’t offer these possible solutions, they aren’t acceptable for me:

Return the MacBook back to the store.
Reinstall MacOS from scratch.

It looks like a problem with graphic card drivers or graphic cards switching

P.S. The Apple Care support doesn’t help me.

Can anybody help with it, please?

MacBook Pro 16″, macOS 10.15

Posted on Jun 13, 2020 8:44 AM

Reply

Answer 1

Aug 3, 2020 5:34 AM in response to dipech

Same issue here. The weird thing is it only started today! Up until yesterday the issue was not happening.

BUT I have noticed it only happens when connecting the monitor via USB-C_to_USB-C cable. Just plugged in a USB-C_to_HDMI cable and the issue does not appear (though refresh rate drops to 30Hz).

Will purchase a USB-C_to_DisplayPort cable and check!

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Answer 2

Aug 12, 2020 6:58 AM in response to maksimt

Your new Mac comes with 90 days free telephone support. Call them:

U.S. technical support: (800) APL–CARE (800–275–2273)

Contact Apple for support and service - Apple Support

Or post an Etrecheck report:

Using EtreCheck to Troubleshoot Potential… - Apple Community

.

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Answer 3

Aug 4, 2020 7:16 AM in response to dipech

UPDATE: when using a Thunderbolt 3-to-DisplayPort cable the issue doesn't appear. It may be due to:

My BENQ monitor doesn't support Thunderbolt 3 connections, only USB-C (they are not the same, apparently)
The 16" MacBook Pro specs say: "Native DisplayPort output over USB‑C", so maybe it doesn't actually like USB-C only (not Tb3) output?

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Answer 4

dipech Author

Level 1

6 points

Aug 4, 2020 7:29 AM in response to Daniel500

Hi, Daniel! It's very interesting. Thanks for your investigation! I haven't tried DisplayPort actually, but I tried HDMI-HDMI and original USBc-USBc with my LG 29UM69G monitor. I don't have opportunity to check DP with my monitor though. Hope it will work for you as well as now.

P.S. I'm selling my monitor now. Apple, it's shame! SuperDuperUltra enormous company can't even notify us that they know/don't know about the problem or they are/aren't working on it.

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Answer 5

Aug 4, 2020 7:51 AM in response to dipech

Keeping the screen correctly updated needs to happen so fast it has been completely relegated to Hardware. That hardware is very fast, and can not become overloaded or clogged (if it did the screen would go BLANK). It updates far, far faster (1/60th second) than the threshold of visual perception (about 1/6th second). What you are demonstrating is unlikely to be a hardware problem at all.

Screen update, especially cursor-position update, is a low priority task handled in the background. The issues you show are far, far more likely to be caused by lack of available CPU cycles.

If you want help, post an Etrecheck report.

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Answer 6

maksimt

Level 1

8 points

Aug 11, 2020 11:18 PM in response to Grant Bennet-Alder

I have the same cursor stutter issue with my 2019 16" MBP base spec: i7, 5300m, 16gb, 512gb.

The stutter happens when my QNIX 3216R 4k monitor is connected via a DP->USB-C, as well as a DP->USB-C dongle.

Testing different monitors: the stutter does not occur when I connect to a Dell U3818DW via a DP->USB-C cable, nor when I connected to a P2717H via a HDMI->USB-C dongle.

Testing different laptops: the stutter does not occur when I connect my QNIX 3216R 4k monitor to my 2017 13" MBP via a DP->USB-C cable.

I am able to reproduce the stutter when running a freshly installed copy of 10.15.6 without any software installed. To be precise, the stutter is reproducible on the initial "set up this mac screen" where you select a language. The stutter doesn't occur in safe boot.

I believe this is either a hardware issue with the R5300M or a driver issue.

This is my second 16" MBP, the first one was stuck in a reboot loop and would kernel panic. I'm really regretting buying an expensive Apple machine. I paid extra to not waste time troubleshooting driver and hardware issues, yet here I am. At least if it was Linux I could try read the source code...

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Answer 7

maksimt

Level 1

8 points

Aug 12, 2020 9:48 PM in response to Grant Bennet-Alder

I got lucky... I managed to update the firmware on my monitor, and this fixes the cursor stuttering issue.

My monitor (the QNIX UHD3216R) had a relatively well known HDCP issue discovered by PS4 Pro Users. The manufacturer released a firmware update to fix HDCP support. After seeing posts that the cursor stutter occurs because of failed and retried HDCP syncs, I thought the two may be related.

I still think the macOS Radeon drivers shouldn't make monitors with broken HDCP implementations unusable. The same monitor didn't have any issues with my 2017 13" MBP.

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