Don't know if I'm alone on this one, but I've experienced this loot bug on the last boss, Rebecca Simmons, when she goes down. Loot rules were round robin, and Rebecca drops a very rare item. When looted, it's Uncommon green, and the loot icon disappears. This has occured on two runs today.
my drop was an uncommon item but it was epic stats so i think its just a bug that doesnt make the items text name purple or call it a very rare even tho it is definitely up there in stats and usefullness.