" * Different egg groups, same genders or No eggs group
The Pokémon are incompatible and therefore will not make an egg. The old man in the Daycare will say: "The two prefer to play with other Pokémon than each other."
this comes straight from Bulbapedia. the pokemon should not have been able to make an egg as they were both the same gender. I did notice that one was a snorlax, who requires an item to get a Munchlax, perhaps that affected something? It's most likely a glitch. Maybe the game miscalculated the dynamic values, as that is what determines a pokemon's gender.