Adding a little more non-technical answer to the question posed.
We kept seeing the recurring error "An item with the same key has been added." in our logs and it seemed to be randomly occurring on calculated members in our UD1 dimension. Several of our UD1 members had api.data.calculate formulas assigned that reference multiple Account.Base ranges. Turns out that a couple of the account ranges assigned had duplicate base members in their respective ranges. We had to make sure that if we were pulling account ranges in member formulas, you need to make sure they are all referencing unique base members.
