I have not had this problem. I try not to let products touch my scalp. The only product that touches my scalp is castor oil and jojoba oil. Have you tried Tresemme Natural conditioner? This is the only conditioner does not dry up my hair. What type of leave in do you use after you co-wash? That is also important. Also, when you co-wash, do you deep condition your hair?
Thanks for visiting my blog. Yes, I do two strand twists a lot. When I do mine, I always do it on washed hair. However, I make sure that the hair has been dried a bit with a t-shirt. To keep it from unraveling I apply my whipped shea butter to the ends and then twirl my fingers around the ends. That always keeps it "locked". I have done my twists with dry hair and I also used the same method.
Regarding washing my twists, I have tried it before, but wasn't successful (Discovering Natural: Co-washing my Twists). I do it ALL the time with Little Sis and her hair stays in tact. If I were to try it again on my hair, I plan to gather sections of the twists, put a ponytail holder at the base of each section, and another ponytail holder at the end of the hair. By putting it at the end, I think that will keep it from unraveling.