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

Running on forge 47.2.0 minecraft version 1.20.1

1. Describe the bug

I can't upgrade backpacks using leather and iron tier upgrades, I thought there might have been a limit to backpacks you could have upgraded but there was nothing about that on the wiki so I think it might be a bug.

2. Write steps to reproduce the bug

I upgraded three backpacks to gold tier and one to diamond and now I can't use iron upgrades on backpacks

3. What is expected behaviour

The backpacks get upgraded to iron tier

4. Screenshots (If applicable)

That's strange issue, did you ever opened these backpacks? or just newly crafted and put in the smithing table?

I just newly crafted them and put them in the smithing table
Weirdly enough it was guaranteed to work when I upgraded them as default backpacks before crafting them into backpack types

Works for me, is it possible you play on server?

no, I play on a singleplayer world

Do you try to apply iron upgrade to leather tier backpack or some other tier backpack?

iron to leather, all the backpacks in the screenshots are leather tier upgrades

I don't know what might cause this, maybe some mod compatibility, could you check with Traveler's Backpack only installed