A small amount of mucus can be "normal", though I never see any with my TP's stool, nor does their stool smell bad. So unfortunately, it does sound like a stool check is in order.

https://azeah.com/recognizing-abnormal-feces

Could be amebiasis* (infection cause by the protazoan parasite, Entmoeba invadens)? if so, easily treated with Flagyl (metronidazole). *or something else?

Did this snake come from a business, a private breeder, or just a pet-keeper that changed their mind?