Can someone explain why this still happens on macOS? I've been using it since Mountain Lion (infrequently though, mainly for some jobs), and on my latest MacBook Pro 2019 (which came new with Catalina then I just upgraded to Big Sur), I installed a 27" Dell QHD monitor, as the main monitor, moving the previous main 22" Dell to the port that the previous secondary monitor was on (also a Dell 22").
I leave the MacBook lid closed, the QHD monitor is hooked into the MacBook's front left USB-C port with a DisplayPort cable, and the secondary 22" is hooked in to the back right USB-C port to an adapter that goes out to DVI. I've never seen any consistency of the problem with ports, cables, or adapters, I'm just mentioning it in case you have. When I first booted up with the new monitor setup, the first (27") monitor worked fine but the secondary monitor (22") remained off until I shut it off and reconnected the cables.
When I restarted this morning, the login screen showed on the secondary monitor, and the alignment was swapped (so that I had to move the mouse pointer off of the left side of the screen to click my user on the right-side monitor). After logging in, the main screen and apps were all on the secondary monitor along with the dock... I had to go into Display settings and re-set it all up again :/ then adjust my windows again. Opening up apps closed by the restart causes them to show on the secondary monitor when they were on the primary one before. This is really frustrating.
Have you found a sure-fire way to prevent this from happening, or at least why macOS Big Sur suddenly randomly forgets display/monitor/window settings after restart? If it somehow chooses order by port... then I'd like to know how it prioritizes ports. Does it have to do with which ports it becomes aware of at the time somehow? As in, it doesn't assume the port hookups are the same and so doesn't wait for them all to become responsive within a few seconds or something like that.
I leave the MacBook lid closed, the QHD monitor is hooked into the MacBook's front left USB-C port with a DisplayPort cable, and the secondary 22" is hooked in to the back right USB-C port to an adapter that goes out to DVI. I've never seen any consistency of the problem with ports, cables, or adapters, I'm just mentioning it in case you have. When I first booted up with the new monitor setup, the first (27") monitor worked fine but the secondary monitor (22") remained off until I shut it off and reconnected the cables.
When I restarted this morning, the login screen showed on the secondary monitor, and the alignment was swapped (so that I had to move the mouse pointer off of the left side of the screen to click my user on the right-side monitor). After logging in, the main screen and apps were all on the secondary monitor along with the dock... I had to go into Display settings and re-set it all up again :/ then adjust my windows again. Opening up apps closed by the restart causes them to show on the secondary monitor when they were on the primary one before. This is really frustrating.
Have you found a sure-fire way to prevent this from happening, or at least why macOS Big Sur suddenly randomly forgets display/monitor/window settings after restart? If it somehow chooses order by port... then I'd like to know how it prioritizes ports. Does it have to do with which ports it becomes aware of at the time somehow? As in, it doesn't assume the port hookups are the same and so doesn't wait for them all to become responsive within a few seconds or something like that.