I have found it, the bug happens soon after loading the save.

WFTO save.zip

Unfortunately I don't know how to reproduce the bug...

I played a bit at 16:9 and then switched to 21:9. I left the HUD scaling at 105% and everything works fine.

I'll update if I encounter the bug again.

It is set at 105%, slightly larger.

I am at campaign stage 5 now, and the same bug does not occur. But then I do not fiddle with option any more.

It might be related to changing settings during game play?