For us, if I heat it to 178/180, it has always worked. I add the starter at 115ish. Smokerbill does 115-120.I heat the milk to 182-185°. What temperature do you use?
I tried to make it with raw milk only heating to 115-120, so I did not destroy the good bacteria, but it has too much fat. I may try again removing some of the cream/fat. I have some separated now, to make butter tomorrow.