Alice has had similar problems - bloody stools that look jellyish. After all kinds of tests, te vets are baffled. I have her on Eagle pack holistic food that is for sensitivity, also it has prebiotics and digestive enzymes. It has improved a lot but not gone completely but she is still eating regular wet food as well - for the simple reason that she doesn't eat much of the dry food and she has to eat - so I give her what she will eat.