That is quite possible that its the shakes being solidified in our bowel, A very reasonable hypothesis.
I wondered also why if people were getting all this mucoid plaque out, why they didnt lose a lot of weight at the same time.
However, I am also curious as to why these 'ropes' come out in long pieces. Psylium doesnt harden that much in the intestines and could easily break apart after the bowel movement. It doesnt stay in one piece. Now you might say that it could be the herbs that make it stick together but I cant imagine that most of these herbs that are used as a laxative would bind something up so tight that it would form 'ropes'. I would imagine that would be painful.
Another thing that I thought of was why these 'ropes' were black! Psyliom is NOT black and you are fasting so there is nothing that you are eating that is black so what could possibly turn them black? The herbs maybe, but there arent really enough herbs to turn all these lengths of 'rope' black.
I dont know. I am not saying that you are wrong but its really something that many people who have passed this mucoid plaque claim that its a real thing as well as many noted health benefits to doing these cleanses. That is a good reason to be hopeful anyway. Its is good to have a skeptical mind though and we shouldnt take everything people say as 100% truth but we also need something to back up what we believe as well. Maybe experimenting with it yourself would give some more evidence to your ideas.