there is indeed a cutoff. there is exponential delay for retrying and at some point lemmy will stop trying until it sees the instance as active again.

there is also a scheduled task running once a week that will delete local activities older than a week. downtimes of a day or two can generally be easily recovered from, depending on latency it can take a lot more time though. if an instance is down for an extended time it shouldn’t expect to still get activities from the entire time it was offline.