Items de-spawning in my inventory

[compact rock]

Me and my friend are playing a vanilla server name Seraphic CS, and items are desponding out of his inventory we have tried everything to fix it from deleting the game to closing app and kill respawning and nothing will work he can put anything in his hit bar without it

[plucky urchin]

You got the rust gods taken your goodies away

[lean galleon]

Thank you for the vid and server name