I don't know if this bug happens with other monster families, but I was playing through Arcade levels, and strange thing happened - Zombie dropped Owlite Feather. I thought that the problem was with Zombies, but nope - after some time (and different level) Mewkat dropped Reaper Rib.
If that somehow helps - I fought Zombies in Graveyard and Mewkats in Cravat Hall.
"2 star materials and higher now only drop from a specific monster family."
Yeah, this seems to be a general bug, not just with zoms--I ran into some t3 chromas last night and one of them dropped a Sinful Brew among other things (description suggests it should be a fiend drop).