ranab This seems like a typical codec error. Usually when codec has an error playing the file, DeoVR will crash and quit. Happened to me many times.
There was one time that DeoVR keep crashing on me, I power on/off the PC and the problem was gone. I think it was due to GPU decoding error.
Now some digging. In DeoVR, are you using "Direct Show" or "Alternative Method"? Have you tried any H264/AVC1 files instead of H265/HEVC files? What about the standard Web videos when you open the DeoVR?
Did you installed HEVC codec from Microsoft? You can see it in "Apps and Features".