New
#11
I'm only a website / phone app programmer :)
Indeed. Unfortunately, that doesn't seem to happen (even with big well known programs including their own stuff, such as Excel, Word, etc). It's certainly a bug (I've reported it to M$ but I don't expect a reply or even a fix, seeing as they can't even fix basic stuff like the Edge shortcut icons breaking after the last update)[General rule for good programed application is that dialog boxes appear on the same screen that app is opened. So if you later move your program on other screen, it will be a mess.
Start with this: open and move your application to desired screen, then close it. When opened, it should start on desired screen and also all dialogs should start on that screen.
As bro67 suggested, my only option may be a full rebuild from scratch
Cheers
Andy