The armor from alex's caves uses a layering system that breaks some models and is incompatible with being hidden.

I posted a video explaining the problem more closely on the alex's caves discord. github won't let me upload screenrecordings here.

https://discord.com/channels/574282697539846164/1027705489141805126/1305614313251143802

the mod used to change the playermodel is figura. It is able to hide the vanilla armor layering and some modded ones that use the
vanilla_model.ARMOR model directory, which the alex's caves models don't

A fix to this would definitely improve efficiency due to not needing to create and render a custom armor layer for each armor set in the mod.