So far I haven't been able to loot Grey items from Robots and the griffin drones. I am not sure if this is the same with every robot since I didn't really notice at first. besides that. when you have the Jhonny clothing and upgrade it you will get a copy in a higher tier when you require the lower tier item to craft it. Also, if it's about the Jhonny items you cannot discard or dismantle them so the copies are stuck in your inventory. Anyway i hope this is helpful for upcomming patches, keep...

BUG not being able to loot Grey items from certain Robots/Drones