RNG? Is that an abbreviation of "range" or does it stand for "random number generation"? Either way, I've crafted tons of cotton cloth yet have never had a consistent problem like this before. And like I said, I crafted (about half a stack) more cotton cloth after I finished the leve, and had no issues. And by "no issues," I mean I was able to hammer the standard synth button and never get below about 60-70 durability, and no destabilizations. I might have just been really unlucky, but the consistency of destabilization and failure for each synth in the leve was unusual.
