I have one female roo I literally named Loner, because she ran off to one stump while all the other roos ran to the other as their home stump.

When I figured out that only stumpmates can mate, I added two males and one female to her home stump. She still won't breed, even though they are all compatible.

OK then I had another female who was compatible with the male of the home stump. He was my fave roo at the time so I gave him three wives to choose from Lol. He mated with two of them but the third, nothing. Again they were all compatible.

So I gave her her own 'husband' and presto they soon had a nest.

Maybe there is something more to it than just personality? Do some of them have certain loner traits? Bit more standoffish? Need their suitor to show up with a heart shaped nibble basket and wearing a tuxedo? ...Or what?