The pups might not develope in the right way or just they couldn't be able to live.
Stillborn pups cannot be used in game neither be revived.
Every time you get a geno, you have a lot of information and one that mentions that the kise is "healthy"; when inbreeding occurs, it may put pups' health at risk: they might have fertility issues or even be stillborn.
Inbreeding occurs when a common relative is present in the first two lines of both parents.
Polukoa shows in the first line for the first Kiseilian, while he's in the third line of the other:
there is NO inbreeding.
Agana shows in the first line for the first Kiseilian, while she's in the second line of the other:
there IS inbreeding.
Currently only the Cursed blood potion decreases the chances to have stillborn pups.