Window Capture, if you resized the window it will affect what is captured in OBS since... the capture is from the exact window size when you first created it as in if you simply resized the height or width of that window if it will affect the source of the Window Capture shown inside OBS. However if you have not changed the size of the window as to exactly when you first created that window capture then I would say that I have never ever seen that before the issue you are having, maybe try recreating your entire setup again in OBS. Maybe try it as clean as in new user settings, uninstall OBS and delete the user settings. Then install OBS again and try testing from new what you are doing of window sources and changing scenes.
Also seems odd an image source assuming that is what you use of overlay is moving on its own too.