Have your parents ever cautioned you against playing with strangers? Red Dead Online makes a great case for those words of warning, as a recent discovery indicates that whatever system used by the game to identify cheaters may lump the people they play with in the same group, and doles out collective punishment.
Reported by one of our readers on the RDR2.org forums, playing in a posse with a player who is in some way altering the game using third party methods - basically, cheating - might get you knocked on your rear just as much as them. If the in-game anti-cheat is triggered, it can not only ban the offender, but players in their posse too.
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It seems that simply being in the same posse isn't enough to incriminate yourself, however. The cheating player must interact with some shared object or entity in-game utilizing cheats to make the punishment affect you too. In the case of user 1LikeRookz, the hacker had sold feathers to the camp which resulted in them being banned as well.
This is an issue similar to the one that affected GTA Online for a long time in its early years. Hackers found a way to spawn or "drop" in-game money, which they could do in a way that you'd be unable to avoid picking it up. When the game's anti-cheat registered the sudden massive income, it assumed you were cheating, and issued the relevant punishment. People having "money dropped on them" would get suspensions and bans even though they themselves didn't do anything to break the rules.
The short term solution is simple - don't join any public posses, and play only with people you know and trust not to be cheaters. If you have a group you play with often already, stick to them and don't set your posse status to open until a solution can be devised!