It's very common for game patches to trigger Windows antivirus. I'd recommend allowing it in Defender.
https://www.virustotal.com/gui/file/0d994964e3cbfe117eb0cfcf0d765d24b13ad2f72229005ae5f72533d2bfaad2/detection
Apologies - I wasn't clear; when I had the quoted issue it was before your fix existed. I was quoting now as I drew similarities between them.
I've now tried again without loading the ultrawide fix at all (I couldn't be bothered to play through the mission a fourth time yesterday) and it still occurs, so it is unfortunately a game bug.
I had this problem with the mission above, and I've just hit a similar one with the Prologue: Act I mission Jim Milton Rides, Again. When I get tackled in the barn and would have to fist fight the chief douchebag, I cannot punch. I can block/dodge and move around, but not punch. I have managed to get out weapons (which isn't supposed to be possible during fist fights) but I cannot use those either.