It seems that NPC sheets when set to disadvantage via 'toggle advantage' are rolling damage as a crit on their attacks. I've tried this multiple times and it seems I'm able to replicate it reliably although it doesn't consider every attack roll made with disadvantage to be a crit just a few so if replicating the issue roll a dozen or so attacks and then try to roll damage on each a few wind up broken and think they're a crit when neither die rolled a 20. The issue also happens more reliably when 'whisper toggle' is on and set to public atleast on my end. This issue is occurring with the standard D&D 5E OGL sheet.