if you enter a brand new world, with just the modpack polygons, do you get this error?
Chances are you're just using too many mods and Scrap Mechanic doesn't like dealing with all the block textures, or you haven't updated your cache files from previous modpacks (to do that just unsub from the modpacks, wait til they are gone completely, then resub to them)

I bet im overloading SM with too many textures
Im using 5 mods and a custom world made from 3 different tiles

Thanks for the feedback!
(seriously that was a really quick response)

I have same issue and i got wrong textures, with 90 mods, when i loaded Polygons first then added the rest of my ♥♥♥♥ it worked? Wtf