I have two Studio Displays and both got bricked after my Mac updated to 15.5. (System Information -> Software -> Installations: shows update to 15.5 and a Rosetta update at the same time. Macbook was in clamshell mode connected to both displays, which I usually leave plugged in to the displays almost all the time anyways). Within the hour of the update, the displays would connect/disconnect one after another in an endless loop. So the screen would turn on, extend my desktop as usual, then disconnect and go dark, then back up again. Mind you, they have been mounted on their VESA mount, working perfectly since the week they launched a few years back. 

To troubleshoot, I tried everything: power cycling, leaving them unplugged overnight, ordered brand new Apple Thunderbolt cables, tried different power outlets and UPS... nothing.

(!!!!) - If you connect to the displays via a regular USB-C cable, the speakers and cameras still show up. I can normally stream music through the display speakers and use the camera from the displays, but the display itself won't turn on. But whenever you use a Thunderbolt cable, the on-off begins and nothing works period.

Whether I'd plug in one display or both, they would turn on (3-dots) and go black, no error message. I'd plug in my Macbook Pro 2023 M3 Max and they would light up and immediately disconnect after 2-3 seconds. That would happen in a constant loop and you'd hear the connect/disconnect chime on the Mac each time and the display would show up and disappear from Displays in Settings.

One user on Reddit posted that he plugged in another Macbook with 15.3.2 installed and left their display connected and it power-cycled and worked after a few minutes. So, I reset my Mac (ugh) and downgraded to 15.3.2 being that this OS version still signed by Apple, and still, nothing. Worth a try. Also, I've always had these running firmware 17.0 since it came out (2023 I believe, so no recent firmware updates, just a MacOS update to 15.5 that caused the issue).

I finally took the displays to Apple Store - Florida Mall. Lugging these is no easy task. They were stumped. After running basic troubleshooting they were unable to "Revive" either of the displays via Apple Service Utility (you can install this app yourself, but Revive isn't available as a self-diagnostic to non-Apple techs). Both displays showed a stable connection via USB-C (not Thunderbolt cable). Apple Repair docs even mention to use a regular USB-C cable for Configuration. Ok. So Macs wouldn't connect. BUT, we connected the Genius' iPad and they lit up instantly and stayed on like there was no issue. I kept saying it has to be a software issue since two displays had the same issue occur at the same time just after the 15.5 update. Otherwise hard to believe both displays would have a hardware fault at the same time. So they agreed that it was software related and accepted both displays for repair. Cool. Note, we also plugged in my Macbook to the store's demo displays and they worked just fine. They also tried using their in store diagnostic Macbooks and a floor model with my displays, and same issue would occur.

I received a callback a few days later saying they want to try replacing one of the internal cables $120 (per display - yikes) or the logic board $400 (per display - double yikes). Again, I felt helpless, and agreed. Luckily, they had another senior tech/engineer in town visiting from CA and they called back a few days later saying it was a software issue and they got the displays working without having to unseal them or change any parts - GREAT! I went to the store this past Monday to pick them up. Plugged in my Macbook, great they work. One of them did not turn on at first, but we unplugged/replugged them back in and it worked. I should have hesitated and stayed at the store a few minutes longer... instead I packed the displays back up and took them home trusting that they've been fixed - ugh.

Key note - The Genius mentioned that the engineer daisy-chained the displays (I wasn't privy to which ports, what type of cable they used, etc.) but they were able to reset the firmware and bring them back to life. The engineer supposedly also had to reset their store Mac to an older MacOS in order to get this repair done. They even advised me at pick-up to hold off on updating my Macbook (lol) so I'm leaving it on 15.3.2.

Got home, set them back up on their VESA mounts... they connected perfectly for maybe 1-2 minutes. And then the on-off started againnnnn! I unplugged them, tried using them one at a time... issue persisted. I immediately called the store back and they advised me to setup a call (called an "RTA"?) with a Level 2 (3?) engineer (folks who actually work on Mac/Displays in CA - awesome). It'd be nice to speak with the same engineer that fixed them before, but we'll see what happens. The call is scheduled for this Friday 7/11. Hopefully they can collect enough data and provide a fix and potentially patch this widely in 15.6 or whatever.

It sucks because the hardware is fine, the store and I know it's software related, and I've spent so many hours on this plus driving to the store back and forth, that the whole experience is brutal. Repair/support options for these Displays is non-existent and you could see everyone trying to stay away from troubleshooting them (although the Genius at the store, she was really understanding and willing to try everything). They don't even have VESA mounts for these lol so we troubleshooted them laying flat on the counter.

So that's my experience. It sucks not having Apple Care on these, but I'm pretty tech-savvy and persistent and would like to get to the bottom of this. That's two displays we're talking about ($$). Apple needs to take accountability and help me refresh the firmware on these and issue an update.