I've had the same issue on multiple setups, multiple monitor types and brands. Unfortunately, no permanent fix, but here is my current work-around in Big Sur: Spotlight Search for "Displays" (or go to System Preferences->Displays) Select "Arrangement" Tab (Next to currently selected "Display") Select "Mirror Displays", wait a second for it to mirror to the external monitor. Finally DEselect "Mirror Displays" and voila, windows pop back to prior location on external monitors and Macbook. Not the best solution, but a couple of infuriating clicks, and at least it's back to the way you had it...until it's unplugged again...and until there is a real fix!