Recently I had a game where I poisoned an arsonist and he survived my poison. There was no way he could have survived that if the game's mechanics functioned as designed. Please read further.
Night 3, from the Arsonist's perspective, you can see he is Poisoned (Article 2). The last Doctor in the game, the only person that could have saved him from this, is already dead (Article 1).
The last remaining protective that could arguably have interfered with the poison was lynched during the day (Article 1) and wasn't even granted the chance to use an ability Night 4 (Article 2). There was no one remaining alive that had any means of protecting the Arson from my poison (Article 3).
The night ends, there is no poison message or survive message. It just goes thru to the next day. The timestamp to witness this on the replay is roughly 18:35.
It is also worth noting that the Interrogator DID die to poison Night 5. That may give the developers some insight on which mechanic is blocking the poison from killing Arsonist.
Attached is a replay for reference. Thank you for reading.
Poisonbug1.SC2Replay