This is a pretty odd one, would be interested in how you got the box so large, but sounds like it just happened when you opened the panel?
One thing to try is to reset your layout - the option is hidden but you can add “Reset Layout” to quick action menu (old ribbon) or a custom tab (next gen) and restart Studio after selecting it to go back to defaults.
Yes, panel locations like find/replace are kept. The question is how it ended up in the state in the first place - you mentioned multi-monitors weren’t part of the equation - what about DPI/resolution changes?