Blight Chest - No Oils/Maps

I thought I might've been mistaking the chests at first, but I've come to realize that sometimes the blight chests in maps simply don't drop oils/blighted maps. I've turned off my filters and there are no items on the ground after opening that would be exclusive to a blight chest. This seems to be happening often.

I noticed it happened with a cartography chest from a blight as well.