Failed to save player data

Title. Whenever me and my friends disconnect and reconnect our inventories are wiped but our chests still contain everything.

[22:48:27] [Server thread/INFO]: xXSatanichiaXx left the game

[22:48:27] [Server thread/WARN]: Failed to save player data for xXSatanichiaXx

[22:48:38] [Server thread/INFO]: sadgirl666 left the game

[22:48:38] [Server thread/WARN]: Failed to save player data for sadgirl666

We are both using legitimate copies of Minecraft.

Yes