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

“My take: Macos cannot distinguish the monitors, because LG monitors (at least those that I have 32UL750) Don't present a serial number and thus 12.3 is only "recognizing"one of them (the one that "answers" first).

The best explanation by far for the mystery issues! However, if true, it shifts the burden on LG to fix (unfortunately!).

Awesome reply and work around.

I agree that there’s been issue with the way macOS handle dual displays for sometime now.

I’m also curious to know how your work around does when both dual displays are connected to the USB-C ports.

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.

That’s good to know that at least it’s working as per (my read of) the spec.

Thanks for updating! The question is, was the previous working a hole that Apple fixed purposely or whether it was an unintended consequence of something else. Even if it was an unintended consequence, there’s no guarantee that Apple will revert it back to something the spec doesn’t support. Only time will tell.

No way Apple is gonna cover for LG’s booboo omitting important monitor ID info. They’re probably ROFL for the poor implementation by LG, which they rightfully should.

The only “solution” is for LG owners to take it up en-masse with LG - i.e. get replaced with new monitors or get compensated otherwise. That could take a while. Shrug.

I read it differently: that is, the spec describes that if you want to have a 5K and a 4K monitor, the 5K needs to be on the HDMI. So it's open to interpretation and the 2018 mini has been working with dual USB-C monitors for 4 years. So I doubt it's a hole. It's intended to work like that, but with Apple who knows.

Also doing a fix is not "covering" for LG or Samsung, is being responsive to the needs of their customer, to return things the way it was before 12.3 in terms of configuration.

I'm just curious about using it with 1 HDMI and 2 USB-C....

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.

I was referring to ambiguous/non IDs that trigger the problem in multiple monitor configurations. That’s a security hole on LG’s part. I seriously doubt Apple will cover for them now that it’s been outed as such. In fact, there’s a very good chance they plugged it. I hope I’m wrong, but I wouldn’t count on an Apple fix to set things back for this LG bug can continue life unfixed.

Maybe, but I doubt it's only LG that does that. If it's more than LG, and a few other USB-C monitors start displaying the same behavior, then they will have a problem (or not - see bellow). The fact the it (or they) works in other OSes is another problem for Apple, as being the only one that requires monitors to have unique device identifiers spitted out over the connection.

On the other hand, I'm curious if the same happens with other Macs with USB-C and without an integrated display (like the Mac Pro). I plan to see if I can get 2 USB-C displays on my Macbook Pro 14, but the integrated display may change the equation here.

Finally, I want to know how the Mac Studio will handle it. Will it present the same behavior? That's something to see and it will certainly affect Apple's strategy (if it's just the 2018 mini, a seriously doubt they will care much for a fix, given that there is a reasonable workaround that is using the HDMI port.

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. 😎

The Mac Studio is n/a to this issue, it’s completely Apple proprietary, like lightning. “Apple being the only one” is their strongest security asset, also arguably their most frequent consumer woe. Since everything is implementation-specific, it’s not surprising that different monitors exhibit different symptoms, especially in multiple configurations.

’nuf said! Let’s revisit after the next release. If it remains unfixed, we can assume it wasn’t unintended.

Conspiracy theorist will argue just that: Apple did it to force people to upgrade their Mac minis to Mac Studios and by Apples new and expensive monitor :) :) :)

I think they have "fixed" it because they must finally "noticed" the monitor swap problem, specially with the Mac Studio with many ports. As usual they can't test with all possible monitors, and I bet they have tested with a few "top grade" monitors that do have unique serials and therefore it worked. But the real world is another story. Not we are not using low end "el cheapo" monitors here. We all probably have good LG (or Samsung) monitors (remember untill the Studio Monitor, Apple used to sell LG monitors). So, it is expected that they fix it.

I don’t know, but my guess is Apple is fixated about constantly tightening security, plugging holes etc. as they get to them. Apple’s new monitor is priced x4 over 3p. Many (most) will prefer living/griping about this issue than forking x4 $$$.

Network MAC addresses are used to identify devices on a network, that is a *shared* environment. Monitor? Not the same at all. I still fail to see it, but to the paranoid eye of Apple's "security" experts it may be.