I also have the same issue with my Login screen and also several other screens in my C6 application. This issue is explained in https://clarionhub.com/t/a-strange-application-behaviour-on-windows-10-creators-edition-1703-build/1262/7
I would suggest you visit the above link. Probably we all are heading towards it.
Reverting back to the previous Windows 10 build 1607 resolves the issue in my case. (This is NOT the resolution to this issue).
I have the following templates:
FM3 4.65
NETTALK 4.46
IP Driver 2.3
CLACOM
ABC Free (One application instance)
RPM: Report templates (6.3)
Taboga barocde
SV’s Graph Global Extension