I fully admit this might be user error but twice now I have only gotten 9 caches after completing all bounties.
Both times I had open space in my inventory so there’s no reason the cache should have fallen on the ground. The first time it happened I retraced the last several zones I was in just to make sure it didn’t fall on the ground. Both times seem to be Act 5 judging by my mat levels, but I am not 100% sure on that.
The second time it happened, earlier today, I was the one who turned in Act 5 bounties so I’m even more confident it didn’t fall on the ground. I still checked the last zone I was in just in case, but again, I had several open spots in my inventory large enough for the 10th cache. One of my party members verified he got 10 from that same run.
Again, I realize this may not be a bug, but considering I had space in my inventory both times I can’t really think of anything else I could be “doing wrong” to cause this. Both times I got 9 caches so the other 4 acts were doubling properly, and I still got the “normal” single cache reward for that act.