At some point characters took damage from an unknown source. The action log indicated the damage, but no source. Only looking at it after the fact did I realize it was probably a trap that I failed the perception check for. The damage roll tooltip was also void of any information. To help avoid confusion, maybe it could indicate it came from an unseen force or location, as this would look less like a bug or incomplete. https://www.twitch.tv/videos/763412078?t=2h33m33s
It looks like quite a few people have had this issue. I might have found out why. Turns out making a jump that should cause damage, but not taking it will store a fall damage value somewhere and give you an "aura of fall damage". Here's a video: https://www.youtube.com/watch?v=2vlVwvDGu6c
Just made a thread about it, hopefully that helps!