Interesting. I’m on an older kernel which may be why I’ve not seen it recur (or maybe I’ve just not played enough VC-1 content recently to notice it).
So I tried the same hardware on Ubuntu 20.04 (previously I was on 18.04) and the hardware decoder fails to open with VC1 (works with other codecs). I wonder if they changed it to recognize the issue and refuse to allow the decoder to open in this version.