0. ALWAYS PROVIDE INFORMATION ABOUT MODLOADER (Fabric / Forge) AND MOD VERSION (For Example 1.19.2-8.2.10)
   FTB Unstable v1.3.0
   Neoforge v21.0.167
   travelersbackpack-neoforge-1.21.1-10.1.3

i'm aware that this version is about a year old.

1. Describe the bug

hi and appologies in advance if it is a duplicate, fixed or related to other mods. i searched for this issue on this git page and didn't find any thread that describes my issue except this, which is kinda different tho,

When slotting a backpack over another backpack. f.e. a gold blaze over a netherite dragon backpack, there is a chance of the tier getting mixed up.

2. Write steps to reproduce the bug

it downgraded my netherite one to gold (which is the reason i noticed), while trying to reproduce it in creative mode, i was only able to upgrade leather, gold and diamond to netherite this way, not downgrade them.
i've noticed no pattern of which backpack is causing this, other than only netherite was involved when it happend.

i did not however test if it impacted the backpacks inventory. either nothing was lost or i didn't notice so i didn't test for that.

3. What is expected behaviour

backpacks should keep their tier. I mean free upgrades are nice, but downgrades are not.
jokes aside, tier upgrades should stay on their respective backpack

4. Screenshots (If applicable)
   don't think so.

thanks for your time and i love the mod (backpacks are great and the effects even better)

You have to check on latest version, playing on older version is pointless, you won't get fix if you won't update anyways