It sounds like is is a sort of 'change-events' pub-subscribe approach, where dependent systems keep their state updated by doing deltas against what they currently store (if I misunderstood this part, the rest here probably is moot).
If that is true, is there anything in the system that guards against if a subscriber fails to ingest an event, for whatever technical reason (bug or systems/execution failure, e.g. network or overload), ie some sort of 'transaction' approach where a subscriber will keep receiving/being due an event, until he has reported back an "ACK I have processed that" ().
I am asking because otherwise it could lead to things like a user account staying open/active, even though an event said it should be deleted.
Some alternative mechanisms with other trade-offs could be things/events like "group X has changed, its current member list is now [...]". In that case, the mirrored group might eventually become consistent on a later update (as opposed to carrying an eternal memory left over by a missed update).
() I am vaguely aware true consistency guarantee is impossible in a distributed system, something about confused generals.