In the past and can be read in the documentation of the plugin:

• Is Hidden is a toggle field. When enabled this kit will not be visible in the kit grid to regular players

This is bugged i assume, as all kits that have a permission are hidden to regular player even when the kits are NOT set to be hidden.

Please fix thanks in advance! :)

'"Show kits with permissions assigned to players without the permission": false,' set this to true.    I'm assuming that's what you're running into

All my "hidden" kits, Admin and NPConly are still hidden and all other kits are showing as normal, use the edit function and check that you have not accidently ticked the box,