Cats' ears can feel hot for reasons that are not medical, but in your case with the ongoing issue I would assume that it might have to do with what has currently been going on.
Baby girl loves to get worse around holidays / when our primary vet is closed. She’s been on a probiotic since the last visit at the ER.. still having diarrhea.. when is cat diarrhea potentially dangerous? Still eating & drinking.. good behavior all things considered and very lovey.
Cat diarrhea is potentially dangerous if it is very severe, accompanied by blood or vomiting, if there is no appetite and lethargy. If it lasts for a couple of days without resolving, you might want to call the vet.