Info:
Forge 47.3.0
Minecraft: 1.20.1

Mods:
Quark-4.0-460
Zeta-1.0-24
QuarkOddities-1.20.1
CuriosQuarkOBP-1.20.1-1.2.5
accessories-1.0.0-beta42+1.20.1
accessories-cclayer-7.4.0-beta18+1.20.1

Situation:
The mod loads and works just fine until the world is left, on rejoining the world the backpack is moved from the accessory slot to the inventory and items stored in the backpack are moved as well.