Losing player and world data

I started a server today, while i was playing there were a few "failed to save player data- aborted" console messages but i ignored them because i didnt really understand what it was. sure enough, my player data was lost after a reconnection. i tried looking around for a fix, first thing i tried was to do a /save-all command before reconnecting, but my player data still reset (logged in naked at natural spawn point.) then i tried restarting the server, but entering the world after that not only was my player data gone but also my house T T .. the seed was still the same as i recognized the area

+ after trying to load a backup, the world is still brand new, but my player data is saving now. am not sure what the issue is/was