I encounter the bug that backpacks turn invisible after reloading of the World.
I still can access the backpack but it have the "Equip button" instead of the "Unequip button" and says "Other backpack is already worn" when i click the Button.
I tried without any other mods, each version of the Mod and different forge versions.
Death seems the only way to get the Backpack back to normal.
A solution for this problem would be nice.

Xaneas

Did you use previous version of the mod on the world?

Just to confirm what Xaneas has posted, I just encountered the same issue on a fresh world.

The mod is definitely still usable; it simply wasn't rendering the backpack, and you can't remove it until death, but it still functions otherwise from what I've seen so far. Also, after 'fixing' the issue with a death and then reloading the world from the main menu, the backpack was working correctly again. It's quite possible that an unrelated crash by another mod caused the issue for me.

Any ideas how can I reproduce?

Honestly, I'm not sure. I had a reproducible crash caused by an unrelated mod, and when I logged back in my backpack was invisible and couldn't be unequipped, as mentioned. I'll keep you posted if I come across the error again in the future.

As additional informations, i tried the following Forge Versions:
14.23.5.2847
14.23.5.2838
14.23.5.2768
Same result on every Version.
Sadly the Mod is not useable because of this reload Bug.