Apps disappear off all screens after external display plugged in

Hey there The Other KP,

Thanks for reaching out to Apple Support Communities. We understand you’re having issues with your external monitor. We’ll be happy to help.

Go through the steps in this link to help with any issues related to using an external monitor with your Mac:

Get help with video issues on external displays connected to your Mac

We hope this helps.

Take care.

Hey The Other KP,

Thanks for that clarification. To verify, does restarting or testing this in safe mode have any impact on this?

Log out, sleep, wake, restart, or shut down your Mac

Start up your Mac in safe mode 

Also, test in a new user account and see if the issue continues there:

Set up users, guests, and groups on Mac

Kind regards.

Yes, I too have this problem. I come and go all day from my MacBook connected to my external display. When I come back to and reconnect to the external display some or all of my apps seem to disappear. But if I use the 3 finger scroll up to see all apps and desktops, I see the missing apps and must drag them to a desktop or they will simply slip away again.

It is seemingly off screen but there is no screen there and I cannot put my mouse there–as in situations when you have an external monitor that is not there, That is not the case, to be clear.