Pals that have vanished are almost always still in the save. The usual cause is the server loading something other than the save you expect, or a mod that no longer matches the game version.
Check for a game update first. Palworld servers update themselves on restart. After an update, mods built for the previous version frequently stop working, and a mod that touches pals or breeding can stop them loading — or keep the world from finishing its load at all. If pals disappeared right after a restart, this is the first thing to rule out.
Turn mods off before troubleshooting anything else. Move any .pak mod files out of the Paks folder rather than deleting them, and switch the UE4SS setting off on the Startup tab. Start the server clean. If the pals are back, one of the mods was the problem and you can add them in one at a time to find it.
Check the world actually loaded. The console shows which save it opened. A line about creating a new world when you expected an existing one means the server built a fresh save, and your pals are still sitting in the old save folder untouched.
Do not reinstall the server to fix this. A reinstall erases the save that still contains your pals.
Palworld keeps automatic backups of the world inside its save folder. If something did go wrong, those are usually recoverable — ask us before changing anything further and we will look at them with you.
If you need help with this, please submit a ticket.