This morning I was one of 4-5 that went in, we cleared the area and went into a Banite temple. Despite killing the Banite boss no key dropped for the chests. We checked outside and inside and didn't seem to have missed anything.
Though possibl that someone made off with the key, I don't think that was the case.
This has been the case for some time now. The one time I've seen the Banite "drop" a key it involved DM interaction, and thus can be assumed to be an old issue unresolved.
Actually, I first reported this issue back in early December last year.
It was subsequently fixed and worked consistently well until recently.
If I had to point my finger on it, it was the update for the persistent storage.
I definitely had it working for me after going to nwn-ee.