this same error plagued me in 8.4. and still does in 1.0.2 and i dont know whats causing it. all i get on start up is:
Failed to load mod "IridescentIndustry": IridescentIndustry/prototypes/logistics-5.lua:63: attempt to index field 'sheet' (a nil value)
stack traceback:
IridescentIndustry/prototypes/logistics-5.lua:63: in main chunk
[C]: in function 'require'
IridescentIndustry/data.lua:137: in main chunk
any help is appreciated

Iridescent belts are mostly copies of turbo belts with a few things changed. That error is appearing because the sprite sheet for the turbo underground belt has been replaced... which is probably because some other mod has changed things. Try disabling Iridescent Industry and looking for the blue text when you hover over a turbo underground belt; that will tell you which mods are modifying it. Then we can narrow down which mod is causing the problem.

well, i have alot of mods that apparently add new forms of belt. but if i have the right turbo belt, its modified by Space Age > 5Dim's Mod - Transport > Bob's Logistics > Artisanal Reskins: Bob's Mods. based on previous incompatibilities, i wanna guess its 5dim's fault
Edit: i have tested, without 5dim's logistsics it gave the same error

If you can track down the exact mod that causes the error I can look into it, but otherwise I can't really help because I can't reproduce the error.

Also, if you have a lot of modded belts already but you want to use Iridescent Industry, you can just disable its belts in the settings.

i just clued into what mod it is, its Artisanal Reskins. upon loading the game without it, i now have a different issue instead with alloy smelting not liking its aai industry compat. but thats a different mod(s) so i'll leave this here

I think this may be a compatibility issue between Bob's and Space Age, because they both define a "turbo transport belt." Iridescent Industry is expecting to find the Space Age version, so when it finds the Bob's version (as reskinned by Artisanal Reskins) it doesn't quite know what to do with that.

Honestly, the best thing in your case is probably to just disable Iridescent belts, since you already have plenty of modded belts.

Well, i have alot of extra belts because of requirements of other mods i wanted to try, Iridescent Industry is no different as i wanted to try playing with Arcanyx. Most of the mods i have though are old mods that are still being updated today, and are mods i added because some old friends of mine said i should try them. So im looking to try new things since some of those "Old friends" i dont talk to much anymore for one reason or another.

Anyway, long story short im going to try this and Arcanyx, over some of my old friends favourites.

Fair enough.

The most common complaint I get about Arcanyx, especially in a larger modpack, is that the Voidcraft and Iridescent Industry mechanics change the rest of the game too much. If that's an issue for you, then you might also like to look at Arcanyx Containment.

Unless it causes issues with compatibility with other mods it shouldn't be a problem for me