How do I make my Studio remember which monitor is which?

Okay, so I just wanted to post this update. After following the instructions below my monitors seem to be behaving as expected. I have rebooted my Studio a couple of times and also put it into sleep mode to test it and so far it seems to have worked. I'll update again if the monitor switching recurs again.

Just a heads up that when you follow the procedure you may need to reset some other preferences. I had to reset my menu bar and Doc.

Here's the instructions I followed

Click on your Desktop, click Go in the menubar select Go to Folder.

Enter this text,

~/Library/Preferences/com.apple.dock.plist

press Go

A new Finder window will open with the file highlighted,

move the file to the Trash, do not empty it yet.

Restart your mac, the file will be regenerated.

Open System Preferences> Mission Control and make sure that box is unchecked.

If the behaviour of Desktops/ Spaces is now working as you would expect, then delete the file in the Trash.

Just a heads up that non of the above actually worked. However, Apple has just updated Monterey this morning on my machine and one of the fixes was the system not recognising a second monitor connected to a USB C port.

Let's hope this fixes the problem..

Still NOT WORKING. I have a monitor connected to the HDMI port on my NEW MAC STUDIO and another connected via USB-C. The USB-C connected monitor didn't even start up just now, after the apple update.

Come on APLLE sort this out

Not sure if this is helpful or not, but I have x2 Benq 32 inch 4k identical displays connected to my Mac Studio Ultra and it has always remembered which is the main display and which is the extended display. I have noticed however that it can sometimes take a fairly long time for the displays to come on and when they do certain application windows will be scaled down and bunched into the bottom left-hand corner of the main display.

Hi,

Thanks for the info.

I’ve tried everything to resolve the issue but so far nothing has worked.

I think it’s a software issue and I’m hoping Apple come up with a solution asap. I know other people are having the same problem.

It's Not Apple's problem.

Your TWIN displays are presenting themselves in their EDID information as the same display. Not similar. EXACTLY the same display. They are not showing different serial numbers in the correct field, and if they did that, this would not be an issue.

Displays from most other makers do not exhibit this problem.

If you did not have the same Model TWIN displays, you would not have this problem either.

OK, so I'm going to ignore the idea that it's not Apple's problem. The last update to Monterey was to address this problem on the mac mini. If I had a toothbrush in my mouth and another up my butt I'd know which was which..

However, I may have found a work around. Whenever I leave my desk for a while I select LOCK SCREEN from the apple menu. So far this seems to work.

as you posted, the serial number field supplied by these TWIN Samsung displays is identical.

UUID is not supplied by the display, MacOS generates it on the fly.

I agree that someone needs to contact Samsung and pressure them to put the serial number in the correct field in their EDID response.

But PC's don't use the EDID information, so there is less market pressure to get it right, unless Users contact Samsung and complain.

That's interesting, I knew others were having this problem.

HOWEVER, let's suppose for a moment that the EDID meant that the mac studio couldn't tell which display was which, and so, on restarting or logging back on, the display arrangement was occasionally switched. Bearing in mind that I have one display connected to the HDMI port and the other to a USB-C port. I could probably live with that. It would be a pain, but hopefully APPLE would fix the issue at some point.

BUT, the fact is, even though I have both displays on exactly the same settings, whenever I log off or restart the chances are that not only will the displays be switched around but the resolution will be reset. And, AND sometimes the secondary display won't even come on. I have to reconnect it to get it to work.

For me this is an issue with Mac OS Monterey. The latest update fixed a similar issue with the mac mini..

The Mac sends a query to the display whenever the connected displays MAY have changed.

This query is only sent at certain times:

• at startup

• at wake from sleep — so momentarily sleeping and waking your Mac may work

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• on invoking Option-(Detect Display) button in Displays preferences (from another display)

Waking from sleep is a time when The Mac is not certain what displays are still connected, so it ASKs. But these Samsung displays LIE TO IT.

I changed to this configuration because of a different problem. Previously I had one connected via HDMI and the other via a USB to HDMI dongle. I found that the HDMI port initialised much faster than the USB-connected one, so when the system woke from sleep, for a short period before the other one woke up it thought it only had one monitor. Unfortunately this period was long enough for macOS to move all my windows onto the first monitor.

That problem went away with both connected by USB, but now I have this problem instead.

Clearly while Samsung shouldn't be reusing serial numbers, macOS knows which port the monitors are plugged into, so identifying them with something like a hash based on serial and port would be reliable enough, but they're apparently not doing that either, or even ignore the serial number altogether. I found a bunch of other reports showing that duplicate serial numbers are common across many different monitor manufacturers, giving all the more reason for Apple to fix or at least work around it.

This is an update to my earlier post. An Apple Studio (Ultra, 64, 8, current OS) uses an Apple Studio Monitor as the center screen, connected via its own port. Two Samsung 27" 4K screens are outboard, left and right, each in its own port, via adaptors. When using two Samsung screens of the model and same year, the two screens presented the same name, and the OS labeled them XXXX(1) and XXXX(2) in the display orientation preference panel. The display orientation became confused on every awake or reboot.

After substituting a same-model but year-newer Samsung screen for one of the outboard screens, the two screens no longer presented the same name; it was like XXXX and XXXY. Since then, the display orientation has remained steady without a single fault; the cursor of course tracks across the three screens as intended.

Unfortunately, there are issues remaining.

A. Dock. Sometimes, the dock, which is supposed to be at the bottom center of the Apple Studio Display, hops to one or the other of the outboard screens. This does not happen every reboot or wake, but perhaps 15% of the time. Opening the dock panel and redesignating its location fixes this... for a while, until it hops again.

B. Assignment of closed desktop files to display. I have placed several files on an outboard screen's desktop. This is to bother me until I file them properly. Sometimes, perhaps 25% of the time at reboot, the location of these files is switched, as between outboard screens, although the display orientation and cursor behavior has not changed. The files do not seem to ever get reassigned to the Apple Studio Display.

C. Assignment of open files to display. If files are left open at shutdown (as one might, to remind oneself what work to start on next time), upon reboot they may not appear on the same screen as they were on at shutdown. This happens most of the time.

These faults are minor, compared to losing display and cursor orientation. They are quickly remedied, and I just live with them. I wish this did not happen. I have no opinion whether the cause of them is the same as discussed in this thread.

None of these faults occurred with two identical, same-year Samsung displays on my old 2010 Mac Pro running 10.14.8, on a 580 with DisplayPort.

Work Around.  I have found a work around to this problem.  I am not enthusiastic enough to call it a solution but it is holding for me after 4 restarts.  I have 2 identical 27" Samsung monitors and 1 X 32" (Samsung also).   The 2 x 27" kept getting flipped after restarting.  From my reading of the forums the problem is identification.  I am not a brilliant tech guy but I thought okay, common denominators.  The 2 x 27" were both using USB c Cables to HDMI.  On the back of the Mac Studio is a HDMI output.  What if I put one 27" monitor to that HDMI outlet.  Now the Mac can see that this monitor is different.  So I have 

1 X 27” HDMI to Thunderbolt

1 X 27” HDMI to HDMI

1 X 32” HDMI to Thunderbolt

All three monitors now are not identical.   After 4 restarts the settings are holding.  

So if this works can I become an honorary Apple Genius?

I hope it works for you, but I've tried that and it didn't last.

My 2 displays are identified as xxxx(1) and xxxx(2). The most common issue for me now is the screen resolution setting. It's 50/50

whether or not it's been altered on start up. The screen orientation has been OK for a while, ie which is the main screen and which is left and right. However I still occasionally have the issue of the secondary display not coming on at all. I have to disconnect it and reconnect it to get it to come on, or reboot.

This issue will only grow as they sell more studio machines. They need to come up with a fix, for instance..

if (display 'A' = display 'B'){

assign id via port connection

}

Question for the group:

Can anyone suggest a list of monitors that are compliant with Apple's multi-display system (and thus won't get confused as to display arrangement, location of dock, or location of desktop files)?

Or, if not a list, what specifications must look for when selecting a monitor?