I’m playing 2 different fresh playthroughs currently with different setups (1. 3 person run, I’m not the host; 2. 2 person run, I am the host), and both times the reputations did not trigger at the same time when turning in quests (for example, the quest when arriving at homestead was handed in by me both times, and only I received the reputation and activated the factions to gain more reputation). The others can’t hand in the quest(s), so the faction only activated later on. Nothing game breaking, just kind of inconvenient.
I didn’t find this bug anywhere, and maybe it isn’t fixable. Apologies if either one is the case.