Well for 1, I’d try to run some debugging/logging on the problem machine.
It could be a windows graphics acceleration problem, but this is rarer today than it was in the 90’s and early 00’s. Reducing the acceleration helped.
If you have debugview outputdebugstring api calls in the shipped program, which can be switched on to capture in debugview or log that would give you an idea of what code is being executed and how far its getting, we dont know how much is being executed at this stage.
It could simply be off screen somewhere with a virtual desktop, or on one of the newer TaskView desktops and API’s for Taskview.
A quick check is the ini file for the window in question. A quick test would be to copy the ini file from a known good pc with the same monitor size and put it on the problem pc.
That depends obviously if you are saving window’s position to an ini and not the registry, although the later can still be cross referenced.
Remote debugging with Debugview.
Edit.
I’m also assuming its the same problem machine, if its not, I’d check antivirus or windows defender settings. Without knowing how much code is being run, we dont even know if the process ie your app is being shutdown by another process/app or service.
Service’s will run with a higher privilege than any administrator, so can do more damage potentially, even DCOM can be dangerous as this can take instructions from somewhere else on the network.