0. ALWAYS PROVIDE INFORMATION ABOUT MODLOADER (Fabric / Forge) AND MOD VERSION (For Example 1.19.2-8.2.10)

Game version：1.20.1fabric+forge
travelersbackpack-fabric-1.20.1-9.1.29

1. Describe the bug
   "Hold a travel backpack, place a set of items into the travel backpack, then fill up your own inventory, leaving only one item that is the same as an item in the travel backpack. Open the travel backpack, move that set of items to your own inventory, close the travel backpack, then open it again—the set of items will reappear."

2. Write steps to reproduce the bug
   The travel backpack on the back is invalid

3. What is expected behaviour
   Copy grouped items

4. Screenshots (If applicable)
   Please watch the video directly

https://www.curseforge.com/minecraft/mc-mods/travelers-backpack

Fixed for Forge - 9.1.34
Fixed for Fabric 9.1.30

the update with fix will be available very soon, I've already fixed that but update also adds furnace upgrades to backpack so it took me a while to add it

https://www.curseforge.com/minecraft/mc-mods/travelers-backpack

已修复 Forge - 9.1.34已修复Fabric 9.1.30

I tried the new version, but found a crash bug，A severe exception was caused by the travelersbackpack-fabric mod, resulting in a NullPointerException. Specifically, it occurred when attempting to access a field in the BackpackWrapper class, as this.level was null.

Could you provide crash log?

您能提供崩溃日志吗？