Originally posted by Interloper-69:

I run my own dedicated Valheim servers. I only reboot them once a week and it always saves the world state before shutting down so simple server reboot wont make items lost.
Client has it's own save, your character and it's inventory. Rest is saved in world save that can be on server or your own computer for single player.
I also run ARK servers and only time we lost some items was when we had to revert to older save due a unfortunate fail on updating a mod that totaled our world. So that was a "reset" to previous state of world.
If some one is "resetting" their Valheim world to some previous save state once a day, no idea why the heck.

My guess is that people who encounter issues like this are playing on dedicated servers that do not save just before rebooting.. at that point it would just rely on the last world save the game did so at most lose 20min since I thing the game saves every 20 mins now. The server I played on most would shut down twice a day at 2AM and 2PM regardless if people were on it or not. Just a forced disconnect.

At least in my testing that is how it seemed to work on the server I played on, but all of that stuff is on the server admin to set up.

If you do have stuff vanishing or duplicating then asking the admin when the server gets restarted/reset for the day/week/month should let you know if that is indeed the issue as the problem would happen around those times. Should be easy enough in ops case to verify that.

edit add- Oh nice, OP sorted it out with how they run the server so all good.