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

Fabric: 0.16.13/0.16.14, MC: 1.20.1
Mod version: Anything after 9.1.25 (tried 9.1.32 and 9.1.33)

1. Describe the bug

We noticed after updating our modpack that the client's couldn't connect to server, it will hang on world load until the client gets the following error:
https://mclo.gs/VAtFjFR#L1762

Upon digging around (duplicating server locally and testing out various things), I found the culpurit to be the Traveler's Backpack mod update, hint was the error message appearing on player connect:
https://gist.github.com/GameBurrow/0011b815d0f9b860e0d5bcd2d83ad2c9#file-latest-log-L5193

Downgrading the mod to 9.1.25 fixes the issue.

I noticed the config had changed a bit, also tried letting the game regenerate the new config and use the new config on client and server, still same.
If I take a clean new server, it works so something must break during the upgrade.

2. Write steps to reproduce the bug

Probably hard to reproduce without our server.

3. What is expected behaviour

Can connect to server

4. Screenshots (If applicable)

https://www.curseforge.com/minecraft/mc-mods/travelers-backpack
Fixed in 9.1.34

Will you be able to check if issue is reproducable with the mod jar that I can provide?

Yep, since I could re-produce it locally with the server files.

Please join my discord server and ping me
https://discord.gg/3dgynxtR

Will you be able to check if issue is reproducable with the mod jar that I can provide?