Yeah, you were right of course, I am running the standard (Google) Fairphone OS. Missed to check the category. (In reply to your withdrawn post!)
So it seems to be a bug of FP Open.
I can’t think of another app I am using that could make it work.
Just great, that VLC works for you.
Btw. what version are you running and where did you get it? Asking because of this thread: