This tutorial is from MC Encyclopedia (MCMOD.CN) using the CC By-NC protocol.

If the title is the topic, the reason is that this MOD has a backpack white list. The default is opened and only 2 backpacks are within the white list. If you want to use all the backpacks

Find the .minecraft/config/bagginses.cfg file and open it

Find B: Whitelise: True to change true to false