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Player Data Corruption

A player cannot join, or is reset, because their saved data will not load. Their .dat file is corrupted, replacing it from backup or removing it (which resets that player) fixes the join.

What does this error mean?
Each player's inventory, position, and stats live in a .dat file in playerdata/. If that file is damaged, the server fails to load it. Deleting it lets the player join fresh; restoring a backup keeps their progress. 
Failed to load playerdata
Most Common Causes
  • A crash or kill while saving player data.
  • Disk full during a save.
  • A mod/plugin writing invalid player NBT.
  • Filesystem corruption.
  • Manual edits that broke the NBT structure.
How To Diagnose
  1. Find the player's UUID and locate their file in playerdata/.
  2. Back up the broken .dat before changing anything.
  3. Check for a recent backup of that file.
  4. Note any mod/plugin in the stack trace that writes player data.
Recommended Fixes
  • Restore from backup
    Replace the corrupted .dat with a recent good copy to keep the player's progress.
  • Reset the player
    Delete the .dat so the player joins with a fresh inventory if no backup exists.
  • Repair the NBT
    Open the file in an NBT editor to salvage data as a last resort.
  • Fix the underlying cause
    Free disk space and address any mod/plugin writing bad data.
Analyze My Log
Frequently Asked Questions

In <world>/playerdata/, named after the player's UUID.

Yes, it resets inventory and position. Use a backup if you want to keep their progress.

Look it up from usercache.json or an online UUID lookup for their username.