Thank you for reporting this issue to us in such detail and providing necessary screenshots and JSFiddles for illustration.
The problem is reproducible on our side and we are currently working on a solution.
The fix will be available in the minor release with the ETA May 6th.
Please let us know if it works for you.
We are glad to inform you that the issue with distinct count aggregation for hierarchies with multiple levels (e.g., year/month/day) was fixed.
The fix is available on our website in the minor release 2.7.5 of Flexmonster.
You are welcome to update the component.
Please let us know if everything works fine for you.