Due to a flaw in the quest design, Ancient Power suffers from two problems:
1) The quest can only be played 4 times, when there are 5 unique items to collect.
2) The quest may radiantly choose the same item twice, resulting in only 3 of 5 items being obtainable.
There's a bit more to fix this than meets the eye (I've looked).
The rewards for completing each step appear to only have 5 levels (base + 4) so there'd need to be a 5th level to the reward. My suggestion would be to either set the default Blood of the Ancients time to 0.5 days, then have the 5 levels above as they currently are. Or make the 5th level have no additional reward.
I would also suggest having a formlist filled at game start with the 5 items that can be collected and used on the radiant alias. Then each time the quest is done, remove the obtained item so it cannot be selected again.
There are some quest variables on supporting script that need to be accounted for too.
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Sorry if this is a bit vague, it's been a long time since I've properly looked at this, so it's mostly from memory.
Very loosely documented here:
https://elderscrolls.fandom.com/wiki/Ancient_Power_(Dawnguard)#Bugs
Issue Data
Issue #29376: Ancient Power - Only 4/5 of the items can be obtained