I host a matrix server and have three friends in it. One or all of them being unable to decrypt messages happens every few months and there’s no easy way to learn WHY do I reboot the server.
Annoying, but the other chat apps have trade-offs I don’t care for.
I've hosted my own synapse since 2019, maybe even earlier. Its the same virtualized instance, all I've ever done is update it. Never had to reboot it other than due to updates.
Nothing in any logs?