warningServer ErrorsAffects: All versions
How to Fix UUID Mismatch After Online Mode Change
Fix UUID Mismatch by renaming player data files to match the new UUID format after an online-mode change.
Quick Fix
Convert player data files from offline UUIDs to online UUIDs (or vice versa) using a UUID converter tool.
Error Message
Player data not found / Inventory lost after online-mode changeHow to Fix
1
Use a tool like NameMC to find the player's online UUID
2
Rename the player data .dat file from the old UUID to the new one
3
Do this for playerdata/, advancements/, and stats/ folders
4
Avoid switching online-mode on established servers
Common Causes
- Switching online-mode between true and false changes player UUIDs
- Player data files are stored by UUID
Diagnostic Steps
- Find both UUIDs (online and offline)
- Rename files in playerdata/, advancements/, stats/
- Restart the server
FAQ
How do I find a player's UUID?
Use mcuuid.net or namemc.com. Online-mode UUIDs are tied to the Mojang account; offline UUIDs are generated from the username.