It seems to be anything I play, but I’m not sure. I originally thought it was a filezilla file transfer issue, but ruled it out because of the player not having the same issue. Your point about some players handling it better brings that back into question.
Annoyingly by it occuring randomly (although at a consistent spot), it’s hard to look for. I have media on this machine I transfered via a hard drive dock, and some via filezilla, so I’ll have to be closer attention to stuff transfered from the dock.