Here is a thought --- this happened to me about 5 years ago. Just out of the blue, my wafer quit sticking. I even went so far as sending a wafer to Convatec (after I called and they send a biohazard pouch) thinking maybe I had a defective batch. Someone from Convatec called and recommended that maybe I should use an adhesive remover. And ya know, it helped a lot. I also added a convex insert, and Eakin seals. The skin around the stoma almost looked shiny, but didn't feel sticky or tacky. Now that I use the adhesive remover pad (like an alcohol prep pad), my skin isn't shiny and the wafers stick really well.
Just a thought --- maybe you already have tried it.
Good luck to you,
Diagnosed with CD in 1979, many resections and meds
Perm Ileostomy July 1984 at Cleveland Clinic
Disease free since surgery