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

Interesting: I've tried to boot my Mini with only the "el cheapo" portable (don't know the brand) and it got stuck. As a "sidekick" to the HDMI connected LG it works.

Definitely there is a bug here. Now we can just hope.

I had this problem on my 2018 intel mac mini after upgrade to Monterey 12.3. One BenQ 4K monitor connected with HDMI, another identical one connected to the USB-C port immediately adjacent to the HDMI port. USB-C connected monitor would not function - not detected - after upgrade to 12.3. I moved the USB-C cable as far away from the HDMI port as I could. Presto! It works. Maybe that connects the monitor to a different bus?

"Maybe that connects the monitor to a different bus?"

I believe that's the case. Regardless, moving the cable to the port that is farthest away from the HDMI port was the only thing that worked for m.

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.

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.

The DP 1.2 "trick" only seems to be working with a limited number of displays--my 2 Dell displays can only do 1.2 anyway, and only 1 screen gets recognized if both are connected via DP.

The only way it works for me: connect a single screen via HDMI, boot, then connect the other screen via USB-C/DP once macOS is fully booted.

I had everything working perfectly up to this 'upgrade' to 12.3, now the second monitor fails to initialize and I must reset into settings after every reboot... and even if doing that, I still don't get the 4k resolution anymore.

Apple, please resolve this!!

Something that used to work like a charm, now doesn't!

Tdbozarth wrote:

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

Interesting as I had the exact same experience. They didn't call me back at the prescribed time, and when I emailed they said they "were busy with another customer". When I tried to pick a new time they ghosted me.

With much effort, I downgraded to 12.2.1 and both of my LG thunderbolt monitors are working again. I will wait for 12.3.x, or whenever Apple acknowledges the problem and fixes it.

This is clearly a bug of macOS 12.3 because before this version my 2 external monitors were working properly. The temporary solution is that every time I reboot I will use the DP port along with the USB-C to activate the 2nd monitor then unplug the DP port.

It’s infuriating that apple released 12.3 with this issue when it was identified during the beta period across multiple versions. They knew about it and choose to release it anyway without a warning to Mac mini users. I expected better from Apple. This issue cost me several hours.

Actually it was the same issue, just manifesting itself differently. When I switched one of my 2 usb-c screens to hdmi to troubleshoot the bug, the hdmi connection would not survive a reboot, I had to disconnect the other usb-c screen first and only boot with hdmi, then plug the usb-c screen, or the hdmi screen would never wake up.

I have the opposite issue. I have a 2019 16" MacBook Pro and everything was fine until I upgraded to 12.3.1 last evening. Now dual monitors won't work and LG Monitor Manager says the monitors I have connected are unsupported. They the same 24" LG monitors I have had connected for years. VERY FRUSTRATING!!