This happens in the case of turning in a quest with a followup from the same NPC. Sometimes, the autoaccept feature is too fast for Questie's quest accept detection.

Yes, this is after a new mouseover.

Were you using https://github.com/Questie/Questie/tree/auto-questing when this happened?

No, i reverted back to default since... that one wasn't finished? :)

Correct. Good to know and absolutely something that we need to check when continue reworking auto questing.