I suspect the Umbra Forma drop from Veil Proxima caches are bugged. There were a few posts of umbra forma drop before Update 27.0.3(from Earth Proxima caches I guess), then in Update 27.0.3 it's removed from Earth Proxima caches, being exclusive on Veil Proxima. I've kept an eye on some big forums for further drops, and it seems no one has got a single drop ever since. I know it's supposed to be a super rare reward, but it's definitely strange: before the hotfix there were at least 2 drops in 4 days, while after it no one gets one in 20 days. It would be nice if you pay an revisit on it, thank you.