I ran into an issue with the backpack for 1.15.2 with the newest update for forge of the mod,
Forge 1.15.2 v4.0.3. I have 3 backpacks crafted and renamed one of the backpacks for convenience using the anvil, also have all 3 on the quickbar slots. I left the game and came back, but one of the unnamed backpacks inventory was wiped and was exactly the same as the named backpack, no crashes or errors though.

This seems so strange, I'll have to investigate