When I used Cascara sagrada it worked slowly and gave me a good bm the next day. I seemed to be becoming dependent on it so have started using Senna. With Senna I get painful cramping at about 6 hours then a bm.
I would guess that Senna is causing your colon to empty without affecting the mass of stool higher up in the small intestine. Both these herbs and castor oil are the only methods I've found to loosen up small intestine constipation but that's not happening with you. Salt water flushes also work well but I don't tolerate that much salt very well.
It is possible that you have some parasites partially blocking the small intestine. Another possibility is that your iliac valve is not opening allowing the food waste in the lower part of the small intestine to move into the large intestine/bowel to be expelled. Years ago an ND showed me how to get that valve to release. The iliac crest is the part of your pelvis that protects your lower abdomen. Place your fingers about an inch inward from the right iliac crest then press firmly down and outward and repeat several times. I would usually feel a sense of relief when the muscle released.