I had pretty much the exact symptoms just recently!
In my case, it seemed to be connected to opening a child window too early in the main frame threads startup code.
- Frame thread loads
- In ThisWindow.Init there was a call to a WindowProcedure (a login window as it happens).
- That login window was behaving as you describe.
The login window was not firing events at all after it opened until you “activated” it somehow. By moving it or possible lose/gain focus. I can’t remember exactly.
My fix was to delay the calling of this window until later, the theory being that would allow the main frame to fully open in whatever way it need, and to also start the login window on a new thread rather than directly on the main frames thread. This also required a different approach in order to retain the “you can do anything until you have logged in” requirement.