I've seen this before, and only since Collections were added (I think?) so I thought it was just about the Collections rewards not handled properly when turning in a collection (can we even do that?) But apparently, this ERROR goes shooting by in World console even when you are turning in your first Quest Complete to Murrar in the QC, where it never did this before Collections.

22:18:02 E Command: Error in COMMAND_ACCEPT_REWARD. No pending quest or collection reward was found

Why is World treating a normal quest hand-in like a Collection? Or are collections now handled in a generic ACCEPT_REWARD case?