I encountered a bug with a quest adding few pawns without faction, here's log message:
QuoteError while processing a quest signal: System.NullReferenceException: Object reference not set to an instance of an objectBio tab of those pawns is blank, message appears in log every time I load the game.
at RimWorld.QuestPart_SetFactionHidden.Notify_QuestSignalReceived (RimWorld.Signal signal) [0x0001a] in <6326ac03f61f45efb3178f3bfd084139>:0
at RimWorld.Quest.Notify_SignalReceived (RimWorld.Signal signal) [0x000ac] in <6326ac03f61f45efb3178f3bfd084139>:0