I've encountered a strange bug on the Sunflower City Streets map 2 different times where the ghost just stops doing everything. No hunts, no quirks, and not a single interaction with anything.
The first time it was with a Power Ghost and I had scene transitioned into it during a hunt (maybe near the end of the hunt duration). It's Ghost Room was the Poll Booth.
The second time was a Weseen and the last thing it did was blow out a candle while I was running back to the van to get more candles. It's Ghost Room was the alley with the garage, Back Alley 3 I think, and the garage had already been opened.