GUI Inventory deleted

Hey everyone

I need help with a GUI of my mod.

I called the item Combatbag and the GIU CombatbagGUI (if that is relevant).

So now i made the guy and i could bind it to the item and it all works fine, atleast for a few moments.

Sometimes out of nowhere the inventory of that specific Item resets (the GUI is empty).

I started a server with friends and now the Item-Inventory resets just out of nowhere.

Sometimes it happens if i switch my gamemode but sometimes it just happens randomly.

Please help me, it is really annoying.

PS: This problem only occures with the Combat Bag. With other GUIs are no issues at all.

Kind regards