currently playing a modset including k2so and a bunch of planet mods including planetaris unbound, after enabling planet arig i get the following error:
Failed to load mods: Error in assignID: item with name 'hyper-underground-belt' does not exist.

At ROOT.recipe.mdrn-superior-loader.ingredients[0].name

Source: mdrn-superior-loader (recipe)

disableing LM:I resolves the issue

after some tinkering i found out that k2so enhancements (null fork) has a setting to tweak arigs hyperbelt might be related, please add a compatibility for arig in conjunction with K2SO(enhancements)

Planetaris: Arig has native support for Loaders Modernized. Unfortunately this is a bug in that support code. I've reported it to the Planetaris: Arig git repo and provided a pull request to fix it. Hopefully it won't take to long to get out into an update.

https://github.com/Syen-ce/planetaris-arig/issues/68