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

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 never turn my computer. It's always on and stay like that (or sleeping) for weeks without a reboot. The only problems I have are that that monitors could swap on return (as I said I used a keyboard shortcut to force another swap - quick and dirty solution) and that sometimes network drives wouldn't be properly mounted/ready for use. For that I run a script on wake-up that remount all my network drives at their "designated" mount points (I don't mount on /Volumes).

I noticed the "same ID" issue when I tried to discriminate the monitors to add an "auto swap if needed" to the wakeup script. There is no way to achieve that. All identifiers macOS provided (even low level APIs) would return the same for both monitors. So long ago I've resigned myself to press "Ctrl-F" (for flip) to swap monitors once in a while. But, with 12.3 I've seen no need to use it. They are always returning in the correct arrangement.

Good work! Looks to me like the dreaded dual-monitor disease, just a different variant…

I would file the bug report and forget about it because dual-monitor bug reports have been in existence since at least 2018. They all share one common feature, which, sadly, gets in the way of Apple fixing them: none of the monitor manufacturers state full compliance with Macs, nor do they offer drivers, updates, competent tech support etc. No putting money where the mouth is. Quite the reverse, in fact, they all take the money and, err, instantly go to sleep, permanently blanking out.

Still, who knows, the next macOS release might reverse this troubled history. All the best.

Lowering the DP version to 1.2 (on monitors that have the option) appears to get around this problem. I had been unable to use my (single) LG monitor over USB-C/Displayport with my 2018 Mac mini following the 12.3 update until I made this change.

I have seen many folks mention LG as the culprit. I have the same problem with my 2 Dells (Dell's displays use panels from AU, Samsung or LG, but the rest is built by Wistron, formerly part of Acer, it's not designed/built by LG).

Was working like a charm until the upgrade, so it's not like it ever was a problem... until now.

Long story short, it's not a brand specific issue, the Mac Mini w/ 12.3 is unable be able to drive 2 monitors off TB/USB-C, period.

Dell U2718Q & UP2718Q here with same problem after 12.3 upgrade.

Circumvention is to run one monitor on HDMI. Lots of winking and blinking now. Not happy.

Had been working fine up until the upgrade except for occasionally getting right & left reversed as someone else wrote either on this thread or the other one.

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....

Both my monitors are DP 1.2, only 1 will work at a time, so it's not a 1.2 vs. 1.4 issue.

I tried a TB to 2x DP adapter, 2x USB-C to DP adapters, you name it, no dice, only 1 display comes to life at a time.

I just bought a HDMI to DP adapter on AMZ to plug one of them via HDMI and leave the other on USB-C, I'll report here if it works.

I suspect the introduction of universal control in 12.3 required significant changes to the graphics/display management layer, and we're all in a what Apple likely considers a fringe case, i.e. not a setup tested before release.

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.

So things kinda work with the HDMI to DP adapter, and I assume it kinda works with straight HDMI as well (I already use all my HDMI ports on my monitor for other stuff hence the need for the adapter for me).

"Kinda works" because the setup doesn't survive a reboot. The only way to make it work is to boot with the HDMI monitor plugged and the USB-C/TB monitor unplugged, then plug the latter once macOS is fully booted. On the bright side, sleep does work, and I hardly ever reboot my mini, so I can live with that, for now. Far from ideal, obviously.

Yeap, same here (and with 2 friends with similar setup): need to boot with HDMI only and then turn the USB-C monitor power on. Sleep "kinda" survive. Once I faced a "monitor role swap" (common with 2 USB-C monitors) with a lost of resolution setting (true 4K -> "default" on both monitors). Also, I've seen the dock reverting to the default config (but I guess it's not related).

The good side: it's really a bug!!!

Downleveling a Dell UP2718Q from DP 1.4 to 1.1a (only option) has me back working on 2 USB-C<->DP monitors on macOS 12.3. The other Dell only supports DP 1.2 which explains why it worked in singleton mode more than the newer Dell and had me just about ready go beat the dog. ;-) Think I'll run down to the local Apple store and beat them up. ;-). Many thanks to the folks who initially made this discovery & suggestion.

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!