It happened to me once as well. IG says its a known bug. occurs if there is an internet hiccup when quitting the game. Something about cloud saves. only work around is to have a backup... which i didn't. or just spawn your stuff back in. which i did.

link to the bug : https://valheimbugs.featureupvote.com/suggestions/191826/read-here-died-but-your-tombstone-is-not-on-server