Likely related to the ongoing DDoS campaign(s) mentioned here:

The problem is that for a couple of hours every day we are under a DDOS attack. It’s a never-ending game of whack-a-mole where we close one attack vector and they’ll start using another one. Without going too much into detail and expose too much, there are some very ‘expensive’ sql queries in Lemmy - actions or features that take up seconds instead of milliseconds to execute. And by by executing them by the thousand a minute you can overload the database server.