benjaminhollon, So this is fascinating. Mastodon stores Home feeds in RAM for performance, and it clears them out when a user is inactive (by default after 7 days). Adding them back when a user comes online is computationally expensive, so it can be problematic for a server if users check in regularly right after that timeout.
At least I found it fascinating; your mileage may vary. ;)
https://docs.joinmastodon.org/admin/config/#user_active_days