@ AA6YQ comments below
+ If you (understandably) cannot diagnose Windows yourself, then I suggest engaging with Microsoft Support to obtain their assistance in tracking down the root cause of this behavior.
I can't help but chuckle at the notion. "Hello, DX Keeper is has failures to sync LoTW QSLs for me but works for others." ;)
@ Try "I have an application that downloads information from a URL. When I run this application immediately after booting Windows, it succeeds. When I run this application after starting other applications, Windows announces that the application has stopped working".
@ You can provide them with the URL if you temporarily enable the "PC has no internet connection" option I mentioned earlier.
@ You can also inform them that the application uses Microsoft's urlmon.dll component to download the information.