I usually make MMF as is and then add color to it. In the same batch I find that after adding some colors (gel form) it crumbles and theer's no way to knead it anymore. Another color using that same batch will be fine.
I forget the other colro but I knwo one for sure was green, I think the other was brown but is there any fix one MMF starts crumbling?
the only two way i know of is alot of crisco, while twisting, pulling just abusing it. also i have added a tiny bit of water, but start very very little, or you'll have mush and have to add sugar, and over and over i'd try the water first, i'm sure you can save it.