I see a bug in Selena which is also present in earlier versions of Idea. I have a laptop. At work I run the system with two monitors. At home use the internal monitor. It may be important that the right left order of the two monitors might not be the default order. I run the Debug window in floating mode on the second monitor. When I take the system home - sometimes hibernating with Idea running although I am not sure whether this is critical, and reactivate, the floating window comes up with an absurdly large width as if a negative integer was converted into a positive very large number.
Resizing the window involved grabbing the edge and REPEATEDLY dragging it as far right as possible than repositioning and repeating. I suppose there is a way to edit the configuration file but that is also difficult and dangerous.
My simple suggestion would be to limit the size of any window to 1.5 or 2 times the current screen width (this is a good idea in any case) and look into the bug causing the original issue.