I've been looking into the problem and I've finally run into the issue myself but I can't seem to trigger it consistently. For the next update, I'll include fullscreen/windowed mode options and hopefully one of those will fix the issue for you as I think it might have something to do with window size. It seems this is a Godot issue unfortunately so it might not be something I can fix though I'll try to provide workarounds if possible.
If the next update (1.2) doesn't fix it for you, I will rebuild the camera system for patch 1.3 and see if that fixes the issue. Thanks for your patience!