I don't know if this changed in 1.23 or 1.24, but I noticed that in the religion conversion window it says that converting to the religion "may" spawn a center of reformation. It use to be guaranteed that the first 2 nations after the initial CoR spawned would get one 100% of the time. It also seems like the usual suspects that would also convert to Protestant or Reformed ( ie Bohemia, Saxony, Brandenburg, England, Switzerland, Scotland) now only do so after having a majority of their provinces are converted by a CoR. In my Saxony game after 1.24, I spread the Protestant faith mostly through war. After the initial Reformed CoR popped in Lubeck, who was already Protestant, Lubeck was somehow able to convert the province back to Protestant before the CoR was able to convert its second province. I never noticed them being attacked or besieged by rebels, so not sure how they converted back so fast. So Reformed died almost right away.