After Monterey 12.3 upgrade, can't run 2 usb-c monitors

I was using an LG monitor as my main screen and a UPERFECT 14 Inches HDR Portable 1080P Monitor on the side, both on USB C.

After the 12.3 upgrade, my 2018 Intel Mac Mini crashed. Even internet recovery was failing. I then unplugged everything and isolated the issue to the UPERFECT monitor. As soon as I plug it in, the Mini crashes. It's not that the Mini can't see it, the machine freezes on startup with the monitor plugged in.

I've unplugged the UPERFECT monitor in the meantime as I have to work and don't have time to troubleshoot, but there's clearly a conflict there somewhere!

Similar scenario here. I'd been running a 2018 mini running Mojave using a super convoluted connection for the main screen (Radeon RX 580 in OWC eGPU -> mDP -> Gefen adapter -> DVI -> KVM -> NEC PA271Q), and an LG 27UN880-B via native HDMI for the second monitor; this setup worked fine, for the most part.

Today I updated to Monterey 12.3, and bizarrely only the convoluted main connection works; I cannot get the native HDMI to show up under any circumstances on this 12.3 install (it still works fine on the 2018 Mini under Mojave, as well as an M1 Mini that is still running macOS 12.21). Even if I unplug the eGPU entirely on boot, the native HDMI output sends no signal at all (it reverts to a "headless" output).

What's even more bizarre is that I had actually done a "test run" of this Mojave -> Monterey 12.3 upgrade onto a cloned external USB3 drive last night, and both monitor outputs were working just fine. Things only got flaky most of the way through the same upgrade performed on my internal drive. Indeed, before this upgrade, I always had to turn the HDMI monitor on to reboot, as the startup and login always went to the HDMI output, only sending signal to the eGPU after booting. Indeed, during the upgrade, the install progress was only displayed on the HDMI screen, but then, about 10 mins before the update completed, display switched to the eGPU screen, and has been stuck there (exclusively) ever since, refusing to even see the main HDMI output.

I'm tempted to re-install Monterey, but with the main screen disconnected / only HDMI connected during install, though I don't want to be stuck on the HDMI screen (I need the KVM functionality for primary display, but also need the second monitor for 4K work).

System Information does appear to "see" the built-in output, but doesn't actually send any output.

Unfortunately, sometime overnight the HDMI connection was dropped, with the monitor not receiving any signal this morning (no display or regular sleep involved, but the screensaver was engaged). I was able to get it to work again using a similar process (power down, disconnect the eGPU, boot under HDMI, reconnect the eGPU), but this is way too much of a hassle to continue dealing with.

I ended up restarting from scratch (well, from a re-clone of my Mojave disk), this time using the Monterey 12.2.1 installer instead of the latest 12.3 installer.

I tried changing to displayport 1.2 but did not help. I do now have left display on hdmi and right on displayport working. Issue now is that the image on hdmi is not as good as displayport. I can deal with it for a bit until this gets solved.

We all need to file a bug report. Otherwise Apple will not care about it. Please do so.

You’re welcome! You’re on dual monitor per spec except for shutdown & restart. That’s livable with since neither are required for routine use, including overnights. In the meanwhile, disable Sleep and let the monitors auto-shut on timer as shown below, who knows it might even improve the shut/restart issue.

I plan to give the dual USB-C another shot, as I can't get the colors on the HDMI to match the one on the USB-C (same model display and I had them professionally calibrated by a friend). HDMI is much warmer.

But in any case if the HDMI+USB-C now solves the problem this the constant swap, I will consider keeping the setup and get the displays calibrated once again (colors will be ok once again). Another advantage of going the HDMI+USB-C route is that it frees a USB-C port for other usage and aside from a display HDMI has no other use. So there is a bonus here.

It worked fine because Apple hadn’t fixed what, if true, appears to be a glaring security hole on LG’s part. Now Apple has inadvertently or intentionally fixed it. Either way, LG has no business making monitors that spit out ambiguous/non IDs and washing their hands off it even after the problem has been isolated to them. The fact that it worked with the flaw in the past is no guarantee it will in the future. Apple are unlikely to give them that pass.

If that security hole was so glaring, why would Apple do nothing for years? If they intentionally did something now, why not announce it in the release notes? And it has not been isolated to LG, as reports about at least Samsung monitors with the same problems come in. Furthermore, the problem is not limited to multiple monitors scenarios. Using an LG (or seemingly some Samsungs) as the only monitor doesn’t work as well.

Paranoid minds would question the coincidence of a significant amount of third party monitors not working with a Mac Mini anymore and Apple's introduction of a new monitor. 😎

AS fas as I understand HDCP compliance and capabilities is exhibited through the protocol and the monitor in question do handle it properly. I'm not an expert on HDCP, but I doubt a unique display ID is a requirement. I'm for one that have used many cheap displays for video playback (that requires HDCP) and it worked fine.

My guess they changed it to solve the swap problem and what we are seeing is a mere side-effect. Will they fix it? We can speculate, but you are absolutely right: we will have to wait and see. macOS 13 is on the horizon! if it's fixed, that it was indeed a unforeseen side-effect. If not, it doesn't mean that it was a hole that was plugged, but just that Apple has ignored the issue. Time will tell.

For the time being all we can do is try to come with workarounds and hope that Apple come out with a fix and that in the future manufacturers start adding serial numbers.

Requirement or not is up to the computer manufacturer. As mentioned already, enforcing strict HDCP is hugely important to Apple because of their high-revenue media library. So I’m sure it’s a requirement as far as Apple’s concerned. Apple may have been lax about it in the past but perhaps no longer and are now enforcing it. While it’s too soon to tell, based on my understanding of Apple’s security emphasis, also arm-wringing 3ps into compliance, the odds are not in favor of a fix. Hope, but keep expectations low.

Ok, I gave the "2 USB-C" configuration yet another try. No go. Zilch!

Next I tried 2 different USB-C monitors and again... Nada! The problem is that the "other" monitor is an "el cheapo" portable one (that I use on the road with my Macbook), that probably also lacks a proper identification. So there is no way to be 100% sure of the culprit here.

That said, time to get back to the HDMI+USB-C.... oh boy, that was a nightmare. Had to perform the workaround twice, and I even added a second shutdown/boot cycle with just the HDMI attached. Sounds like it needs to "record" which monitor is booting (seem to remember). If the mini boots on the USB-C it will not work. Need to boot on the HDMI. Why? No F clue.

Aynway, this behavior with different monitors makes me believe that there is much more going on under the hood here. But right now I'm happy that I can get both monitors to work, sleep/wake seems to be working, I'm seeing no screen positioning swap and I have an extra USB-C port (add a second external drive?) free. I don't mind the setup but the color profiles are not matching. I need to perform a new calibration, but for most uses, it's ok (bugs me because I use an 8K wallpaper over 2 4K monitors, so I do notice the difference of the color tones). But that is solvable (and I can live with that).

Will see what happens with the Mac Studio, soon!

I've also seen this on el cheapo USB-C monitor. Would not work even when running solo.

I'm starting to think that this is not related to the fact of equal ids, but rather something they had done that actually broke it. So we should all open bug reports.

I'm also seeing a lot of flickering and color screens (sometimes green, sometimes red stripes) when booting. Also, returning from sleep is now really sloooooow (HDMI + USB-C). But I can live with it.

Will try the suggestion to bump the DisplayPort (and USB-C) protocol versions to 1.2 (from 1.4). One thing I know is that it will change the color settings....

Definitely we are on a fringe case. I suspect they have always considered/tested the Mini in an HDMI solo config ou a HMDI+USB-C combo. Let's file bug reports and hope they listen. But I will keep my expectations down, considering the track record of them fixing Display detection bugs.

I have same issue w/2 LG 5120 x 2800 monitors. Worked fine since mini launched now I cannot get second monitor to work. They are both connected via usbc. Previously they were on same bus but I moved one connection to other bus since I read here that this was important. I have had two calls w/Apple support so far yielding zero results other than 1) being abandoned by senior advisor who scheduled a follow-up meeting and then ghosted me and 2) having a second senior advisor schedule a genius bar appointment. Everyone wanted me to do invasive crap to my system but when I mentioned that there are several threads on web about this being a broad issue and asking when in the process to they acknowledge the broader issue and engage engineering team in an answer - their reply was "we do not even know yet that this is a problem with the mini - so all engineering is going to do is ask us to run these tests first." I get that as a standard response however when someone tells you there are many reports on this on the web you think they should/would have a different response.

So, I will take my mini to Apple Store in a few days, they will likely make it work on something they have ... then what? I have to buy new monitors? Nope. If that is my choice I will buy a PC.