https://imgur.com/a/i0tkM2i
Potion Master was able to kill Coven Leader.
There was a Mayor, so no Transporter.
According to Coven, it said in their chat that PM had chosen to investigate the Coven Leader (To my knowledge, it usually gives you a message like 'You already know this persons role'), I've never experienced it saying about another Coven member investigating another.
So there's some sort of bug based around Potion Master that allows them to investigate and kill their team?