There is a problem where the world will begin and sometimes gives me the achievement "Maximum Capacity!" and unlocks all the slots... with no effort. No trophies, no nothing, just sometimes it will do this and sometimes it wont. I am using a modpack, but none of them affect how your armor works. Also, if it helps, when I die in survival it resets and the mod works just as planned.

If you need to contact me, definitely do it at my Discord if possible. If not use this here :)
Discord saty#9411