Thx… yeah the mouse Y stuff doesn’t get called anywhere in my blueprints. Maybe I have to check my C++ classes again.
You’re right, it is no inherent problem with the 4.21 build. It is just that the 4.21 apparently did something new in the source code (maybe something with the input) that interferes with my code and/or vice versa. I checked my project with 4.20 again and it all works there.
I think I have to study the 4.21 release notes. Thank you guys.