Hi
We recently installed this mod on our server and after changing our nicknames in game and re-logging our characters were blank (new colour, original name, empty inventory)
The character files are still there because trying to change the name again changes it to [new name]#1
The nickname change does not retain after re-logging and the character file becomes locked under the new name

Thanks for the report!
You can use "/swap-players <player> [player]", "/permissions" and "/open <player>" commands for returning inventories. (source)

I will fix that bug soon

Fixed and you can check it again because everything works now perfectly. (but if you play in LAN then... everything can be complicated)