It's not that strange. A timeout occurs on several servers overnight, and maybe a bunch of Lemmy instances are all run in the same timezone, so all their admins wake up around the same time and fix it.

Well it's a timeout, so by fixing it at the same time the admins have "synchronized" when timeouts across their servers are likely to occur again since it's tangentially related to time. They're not likely to all fail again at the same moment.

It's kind of similar to the thundering herd where a bunch of things getting errors will synchronize their retries in a giant herd and strain the server. It's why good clients will add expenses back off AND jitter (a little bit of randomness to when the retry is done, not just every x^2 seconds). That way if you have a million clients, it's less likely that all 1,000,000 of them will attempt a retry at the extract same time, because they all got an error from your server at the same time when it failed.