I develop Construct 2 on a dual-monitor system and have never seen such issues. Can you provide a series of steps to follow that reliably reproduces this?
I use a tri monitor setup usually like so:
|.....monitor A....||...monitor b...|
..............|...monitor c....|.............
So monitor C is below A and B, and in the middle. I use Construct on monitor B. Dialogs are getting lost in the space to the right of Monitor C.
No other applications do this that I have noticed. I have to do a series of monitor adjustments (switching main monitor) and resetting dialogs in Construct for it to work right...even then it is finicky. I cannot reproduce it constantly...but when it occurs, I end up having to force shut down construct (end task) because I cannot see the dialog open...and I cannot save with a dialog open.