I may be Pooh obsessed, but it might be helpful if you asked to see his stools. When I was not absorbing properly, sometimes it looked more like Crisco in my stools, with oil floating on top. I am guessing this is one sign of major malabsorption,when you stop absorbing fats because it only happened when I was in a real bad way, and would be a bigger red flag for me. I see mucus often, usually I get a little unfermented dairy in my diet, or I have a cold or something, and I have seen this with the Grandchildren more often. It concerns me for them, they tend to run low grade night temperatures, one has had tummy surgery and they complain with tummy aches. Being a Crone, it scares me, but I think it's mostly a lactose thing, and their Doctors do not seem concerned, but they do check stools for blood on the girl who had surgery for intussusception.
I am inclined to agree with EMom about probiotics and limiting carbs, but I would also try to avoid any unfermented dairy, and add good quality yogurt. I hope and pray he is well, and this is a passing thing. I think sometimes the flora in the gut gets out of balance due to a viral infection or something and then in a few months, or with diet modifications, things return to normal.
Crohn's for life, symptoms included terrible joint and soft tissue pain, just met first cousin who suffers from Reiters-explains sooo much. Great control on SCD (when I'm good) and I get by with a lotta help from my friends!