Multiple users and disconnecting external display

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and reboot normally. Then test to see if the problem persists.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

This problem might be related to changes in how macOS handles display management in newer versions. One potential workaround could involve adjusting the display settings for each user account individually. You could try setting the display resolution and arrangement separately for each user account to see if that resolves the issue.

Another option to explore is resetting the display settings for all user accounts. This can sometimes clear any lingering issues with display configurations that may be causing conflicts between user accounts. However, be cautious with this approach as it will reset all display settings to their default values.

If these solutions don't resolve the problem, it may be worth reaching out to Official Apple Support for further assistance. They can provide personalized support and may be able to offer additional insights or troubleshooting steps specific to your situation.

FWIW, I could not reproduce this on my mac (2019 16" MBP) on my testing.

I used Fast User Switching between accounts, then disconnected the external display, and did FUS back to the first account. It adjusted normally, just it would if disconnecting the display when having a single account logged in. The dimensions were correct and windows from the external display reverted to the internal one.

Are you by any chance using the display as mirror of the internal? When I tested this, I had the external display as extended desktop. Maybe that is the difference... I will test that and report back.

mbne wrote:

Display is a second display (primary I think) not mirrored. But these are M1-based Macs so perhaps that's the difference. Nice to know it's not a "feature" of Ventura/Sonoma (which I'm assuming you're running).

Yes, I am running Sonoma 14.4.1.

I also have access to an M1 Max, but only at work, and it usually has only one display. I will see if I have a chance to attach a second display and test, but not today (it's a national holiday in my country). I will report back.

Also in mirror mode, it is working correctly here.