Would be cool if fuel converters could work even when player is away.

No worries; I appreciate you taking the time to help chase down the issue.

Huh. Well, with that knowledge in mind I've gone and retracted my statements on those mod pages. Looks like more investigation is necessary. I'm sorry for the trouble.

Looking at the files of the mods, Mech Overhaul and Cosmetic Slots both override mechpartmanager.lua, so it's honestly pretty impressive that it's not just a hard-crash every time. From the logs I'm looking at, it seems like the items are failing to instantiate (i.e, becoming PGIs) when one of the mods tries to retrieve information that doesn't exist, presumably because the other overwrote the necessary files.

In other words, Overhaul and Cosmetic Slots are very incompatible in theory, and I would call it a happy anomaly when they do work together.
My mod doesn't lay a finger on any of the material related to the crash, so my best guess would be that installing this changes your load order just enough to disturb whatever improbable balance allowed the two others to coexist in the first place.

That's curious about the reported issues, as I've had both mods installed for much longer without issue, but when I nabbed this one ghe other day the mods broke until this one was removed.

I haven't tried it with a new character, however. I only tried it with a game-complete veteran character and noticed the problem.

It's also worth noting that the reported conflicts predate this mod by almost eight months.

Do you experience any issues if you use them in a new/pre-mech character? Cosmetic Slots overwrites Lua files and seems to mess around with item buildscripts, so I'd extremely surprised if installing mid-save didn't cause problems.

My game didn't crash, but with Mech Overhaul, Cosmetic Slots for Mechs, and this mod installed, my mech became inaccessible as it converted all of the parts in use (except for the horn) into Perfectly Generic Items. When I uninstalled this mod, those parts reverted back and became fully functional again.

A bunch of people are reporting Mech Overhaul and Cosmetic Slots for Mechs as incompatible lately on both of their mod pages, but I think the likely culprit is this mod and players not realizing it if they've installed it.

Do you have further information? I just tested them together, and I got a initial crash from installing Cosmetic Slots mid-save, but afterward it appears to work perfectly fine.

It appears this mod is incompatible with the Cosmetic Slots for Mechs mod.