Why Homemade Goetta Won't Set

Pre covid I was in Cincinnati and fell in love with Goetta, an oatmeal based scrapple. I cannot find it in the DC area so I started to make my own. The basic recipe is 3 cups of Irish steel cut oatmeal (or pinhead) in 8 cups of water. Simmer covered for 2 hours. Add a pound of ground beef and a pound of ground pork and some salt. Stir it in and cook covered for another 1 - 1 1/2 hours. I have started to use a heat diffuser since the oatmeal was burning to the bottom of the pan (gas stove). So only twice I have gotten it correct. The other 20 or so times it did not set up or set very loose. Or it has a meatloaf texture, like I cooked it too long. It still tastes good and I deal with it but I would like a consistent product. I use a good fatty pork but an organic ground beef with a lower fat content. Is less fat an issue? I have made scrapple but since that is corn based the corn gluten seems to set up consistently. Any thoughts?