Hello! Today I popped these three puppies:
https://www.lorwolf.com/Play/WolfDetails?id=295508
https://www.lorwolf.com/Play/WolfDetails?id=295509
https://www.lorwolf.com/Play/WolfDetails?id=295510
508 and 510 are identical EXCEPT for the sex of the pups. After speaking with others on the Discord, it appears that opposite sex twins have triggered the achievement before. Initially I thought, if sex doesn't count, maybe the achievement is only comparing sequential IDs, but after discussing on Discord, these wolves triggered the achievement and they are opposite sex and non-sequential:
https://www.lorwolf.com/Play/WolfDetails?id=287720
https://www.lorwolf.com/Play/WolfDetails?id=287722
(The patterns have been changed since birth.)
I popped the puppies on FireFox on Windows if that potentially matters!