Minecraft Version: 1.21.1
Apotheosis Version: 8.0.1
Modpack: All the Mods 10, v2.13

Relevant issue from the ATM Github page.

Items that can be both placed and worn as armor, such as the backpacks from Sophisticated Backpacks, gain and lose randomized prefixes and affixes when placed and mined, as if they were pieces of equipment. Reproduced on three different mods:

Sophisticated Backpacks (backpacks are wearable as chestplates):

Jonn's Trophies (trophies are wearable as helmets):

Simply Lights (lights are wearable as helmets):

I also attempted to reproduce it with a placeable item that can't be worn as armor but can be worn as a curio (the Infinity Backpack from Industrial Foregoing), with no results. This seems to only affect armor slots.

This Issue can be temporarily solved by changing config file. However maybe this suggestion could solve mod compatability problems better,

This is the result of the affix conversion loot modifier

However it includes a 0% chance entry for loot tables with blocks in their path, which blacklists them. I'm guessing these modded blocks do not follow the vanilla convention.

I just tested and confirmed this behavior in Craftoria 1.11.0, which includes Apotheosis 8.0.1.
From what I know, Apotheosis will automatically reforge item drops for free if (a) the item to be dropped can be reforged at the Reforging Table and (b) the item to be dropped does not already have a rarity and affixes.