M4 Pro Mac Mini Persistent DCP Kernel Panics with LG OLED (TB5 / DSC / 480Hz)

I honestly don't think this is a software error. You have panics in all different places for all different, MOSTLY display co-processor related and one sleep related problem. I think you have a hardware issue.

¿What is the date of your most recent backup, and by what method?

You MUST have a Trusted backup before submitting your Mac for service. if the mainboard is swapped out, the boot drive will be swapped out as well, and you will not get your files back.

Once you have a trusted backup. I recommend contacting support. See my next post for the "Big Picture"

Debugging steps: please read everything before you DO anything

General debugging tips:

Make certain you have applied all available software updates, because no one wants to debug a problem that might have been seen and solved already.

Then you need to go through the “regular" steps to eliminate added software as the cause of the problem:

• Run In Safe Mode, where no third-party add-ons are loaded

• create a new "clean" User account, and run with that to eliminate contamination in your regular User account

• run the diagnostic to check for GROSS issues. "no fault found" is not the same as "all is well".

Use Apple Diagnostics to test your Mac - Apple Support

https://support.apple.com/en-us/102550

If you are seeing kernel panics, post a panic report. Some panic-reasons suggest a Hardware issue. There is a procedure that can allow you to find those reports to post one. Ask for assistance if you need it.

Genius Bar:

if you take it to an Apple service provider first, they CAN run their diagnostics, which are a bit more comprehensive than the User diagnostics. In the very small amount of time they are run, “No faults detected” still does not mean “All is Well” but at least there are no detected GROSS problems. Unless they can find a fault, they will return your computer unchanged. Genius Bar technicians are NOT trained to read panic reports and computer logs.

When you present your computer at the Genius Bar with the expectation of a quote to repair it, you must generally meet these criteria:

• your Mac won't do anything

• your Mac fails diagnostics

• your Mac has a problem you can repeatably demonstrate on demand

one other oddball case:

• Apple online support has DIRECTED a Service Provider to replace specific components inside your Mac, such as the mainboard or display. Bring proof, such as case number.

Telephone Support:

The telephone support people are more likely to work with you. They will insist that you go through the motions to eliminate software issues. But when they get to the end of their list, Do NOT allow them to tell your it’s fine or there is nothing more they can do for you!

You should insist on having your problem escalated to a specialist. Specialists are more likely to actually read your panic or other reports. If still no resolution, ask them to start a formal, tracked Bug Report on your behalf. If they think this might be a Hardware problem they can DIRECT an Apple service provider to swap things (likely mainboard) for a new one.

Apple support does appreciate what we do as Volunteers here on the forums. They can and should read what has already been posted. Be sure to tell them where they can read it. But they do NOT take our conclusions at face value -- they have their own more rigorous procedures they follow.

You MUST have a Trusted backup before submitting your Mac for service. if the mainboard is swapped out, the boot drive will be swapped out as well, and you will not get your files back.

"panicString" : "panic(cpu 0 caller 0xfffffe004ab53178): DCPEXT0 PANIC - Unsupported number of horizontal slices for DSC \n - iomfb_ap_callee_0(26)\n Unsupported number of horizontal slices for DSC \n\nRTKit: root

Hi Bostonhack,

Thanks for the update.

My unit was manufactured in March 2026.

What makes me doubt that this is a Mac hardware issue is that my Mac works normally with an MSI monitor. The problem only happens with the LG 27GX790B-B, and in my case it is 100% reproducible. Because of that, I also suspect this is more likely a handshake / compatibility / software issue between macOS and this specific display.

I also tried lowering the refresh rate to 60Hz, but that did not help. When I connect this monitor over HDMI or TypeC-DP, macOS does not even get as far as recognizing it as an external display. The Mac simply restarts immediately. After rebooting, Diagnostics Reporter pops up and shows that a system crash occurred.

I contacted LG support and was hoping that maybe a firmware update could solve it, but I did not get any useful guidance. They basically said they had no concrete information, no firmware update available, and no specific compatibility guidance.

What makes this even harder to understand is that this monitor is not advertised as incompatible with Mac. It is difficult to imagine that an issue this severe would not have been noticed before release.

That could be caused by a Hardware failure of the DCP Display Co-Processor.

Another possibility for failures that produce a decided non-trend is a RAM memory failure.

MacOS randomizes the initial load point of its software, as hedge against fixed-address attacks, and that produces a non-Trend as the bad memory cell moves into a different routine or holds different data.

Regardless, this is too complex for Volunteers to diagnose here. Check those suggested procedures and contact support to have a specialist read your reports. Maybe you can get a Bug report named after you.

information I could find easily suggests the LG 27GX790B appears to be a 2560 by 1440 display capable of HDR 10 bits/color at 54 to 540 Hz.

interfaces include:

2x HDMI 2.1

1x displayPort 2.1 with DSC

1x USB 3.2 upstream with DP alt mode

when using the display's USB-C input directly, data is limited to the highest standard data rate that fits inside a 20 G bits/sec envelope, which is HBR2 at 17.28 G bits/sec. That could support up to 141 Hz Uncompressed, with standard timing, and likely up to 240 Hz with DSC.

IF the display had a Thunderbolt-3 or -4 input it could go up to 205 Hz without compression, and if the display has a Thunderbolt-5 input it could conceivably go up to 516 Hz without compression.

That was not intended as a challenge, just a request for a bit more than the top-line information from a pertinent panic report. I ask because the re-organized 'human readable' panic information is often presented farther down the page(s). (Once the report devolves into incessant software-names or incessant Base-64 dumps with lots of AAAAAA lines, you are done.)

Try the first few pages of the one that refers to:

DCPEXT1 PANIC

<< I have been posting the panic reports, though you get no feedback... >>

The agreement you assented to when you said, "OK, share my panic reports with Apple" says that those are anonymous reports. They may be tabulated, but they do not contain any contact information. They could not contact you from those, even if they wanted to.

The difference between an AI bot and a person is that a person "has feel for what is hardware-related"

An AI bot knows what the typical problem is, and nothing more.

Apple telephone support can get you a Specialist to read those reports, but you have to do most of the stuff on my list first.

Contrary to conventional wisdom, DO NOT re-install MacOS, because you will lose your stored panic reports. MacOS after Big Sur is on a crytpo-locked snapshot image, and if it were damaged, it tells you it is damaged and must be re-installed.

I’m seeing a very similar issue, although my setup is a bit different.

I’m using a MacBook Pro M2（macOS Tahoe 26.5） and an LG 27GX790B-B. When I connect the monitor over USB-C, it works normally and I do not experience crashes. However, as soon as I use HDMI with this monitor, the Mac becomes unstable and crashes.

I haven’t found a permanent fix yet, but I can at least confirm that you’re not the only one seeing serious instability with the 27GX790B-B on a Mac.

Rather than a pervasive issue in macOS, this suggests a possible hardware problem is your M4 MacBook Pro.

please post the entire panic report, using the "additional text" icon in the reply footer.

"panicString" : "panic(cpu 2 caller 0xfffffe0049347178): DCPEXT2 PANIC - power_down_M3: auto_mode_change failed with 0x8000000f - iomfb_ap_callee_0(26)\npower_down_M3: auto_mode_change failed with 0x8000000f\nRTKit: root

"panicString" : "panic(cpu 0 caller 0xfffffe004b4df038): DCPEXT0 PANIC - apt firmware: video_mode_main_init.c:195 main_init() -- - iomfb_mailbox(72)\napt firmware: video_mode_main_init.c:195 main_init() -- \nRTKit: root