A friend of mine is running a Sevtech Ages server, and everytime one of us sleeps on another planet it crashes the server.

Crash log: https://pastebin.com/d7DmfHzK

The crash doesn't happen instantly, (takes about 5 minutes), but always happens after sleeping in a cryopod.

That is because Galacticraft does stupid things with World tick time, and negative values. You are presently four versions out of date, please update astral sorcery to the latest, as multiple issues involving Galacticraft dimension time has been fixed in between the version you're in and the most recent.