From another thread:

Originally posted by Xenia26:

This happened to me. Here's what i did fellers.

First open your game and when you're on the main menu you'll see a tiny white bar on your lower left hand side of the screen. If that's not there. Then do the following.

Open up file explorer, and go to your C: drive. Go Users -> (The user you are) -> appdata -> Local low -> Irongate -> Valheim -> Characters.

Now that you're in the file location you should see a list of all your characters. If your character if in here you'll see the files are ending in either .new .vdf .old or just .fch.

Your real character file will be a few thousand KB in size. You guys most likely don't have the exact character as before but an old copy of that character, hopefully only a few hours old.

For instance, say the character you want back is named Bob Jones. You'll see a file named (Bob Jones.fch.old) All you'll need to do is rename it. Simply remove .old from the end making it look like (Charactername.fch). Launch your game and see if your character is now there.

I'd really recommend making a secondary folder on your desktop just for world / character backups and after every session backing up your data. Make sure to save a few just incase. Hope i helped <3

It's been happening to others so I'd suggest you post about this on the bug forum, maybe add to one of the several existing threads instead of making a new one. Explain what happened, anything odd or crashes. This is something the dev team will want to fix quickly, the more info they can get the better.