I've bred "zillions" of mice, rats & hamsters, but never ASFs. However, it's a bit like waiting for water to boil when it comes to the first litters. It matters if these are mature enough, or only just getting there- and new homes are stressful for rodents too, especially if there's a lack of privacy; from what I've heard, I think ASFs are the most particular. New colonies of all kinds usually take a bit longer to get going, then once they're breeding, you have the "opposite problem". I hope just a little more patience is all yours need- a month & a half isn't all that long for new animals.
Off-hand, I'm not sure that cat kibble is the proper diet for them? But even if it is, you still might want to add some enrichment, nutritionally speaking. For example, I share bits of raw kale, carrot, & apple with my mice on a fairly regular basis; also nuts & seeds, especially in cold weather. I wouldn't be so quick to replace any of them, especially if they seem to be getting along.