So the title is probably a little confusing but here's the full description.

We installed this mod knowing that mated bonuses would be a little whack, so let's sort the animals into pre-patch and post-patch animals.

We bred 2 post-patch argentavis together, generating a new animal. This new animal can't breed with post-patch argentavis(es?)(i?), it can however breed with pre-patch argentavises. (I would assume further bred animals as well).

Not too critical of an issue since I'm assuming future bred animals will be just fine but I'll update as neccesary.