I am having almost the same exact issue with my 6 year old cat leela. It start about 1.5 months ago they figured she had a bug or it was stress from our new kitten (shes a bit sensitive) but shes eating normal playing drinking and cuddly. The vet gave her a probiotic and antibiotic and shes had soft stools since but I noticed blood in her stool again this weekend and it looks exactly like your cats. Next we are going to take a sample in but we are puzzled what is going on and I am worried sick.I got an appt for Tuesday. With the Covid-19 restrictions in place, my vet (plus many others) is not allowing us to go inside. The vet tech comes out, gets the pet, when it’s our turn we communicate by video call or phone if the person doesn’t have a form of video calling I don’t like it but I understand. This only for scheduled visits. I don’t know what they’re doing about other situations.
So here is what his feces looks like. It’s only about an inch long. The blood was more mucus like when it first started, now it’s just blood, no more mucus.