Why "Cardinality Aggregation - Date Histogram" lacks precision at particular date?

Elastic Stack Elasticsearch
1

I am using "Cardinality Aggregation" on "Date Histogram".
And I found one weird result.

I already know that "Counts are approximate", so the precision is not 100% accurate.

But when I draw the "Date Histogram" only one particular date (ex. September 11th) is very inaccurate compared to other dates.

I've tried computing the exact unique count.
Other dates except that one date are accurate enough. Weird...

FYI,

  1. Doc counts are almost similar each date.
  2. Docs are in the same index (3 shards, 1 replica).
  3. Docs are inserted in datetime order.

Now, I wonder about the inaccuracy behind the scene.

Could anyone explain this?
Thank you.

2

It's hard to comment on this without more information unfortunately. Maybe at a first step you could paste the response for your aggregation into a gist (with the weird date bucket marked) and link it here?

3

I am very sorry. It was a stupid mistake. Now, it's working fine.
Thank you very much for your attention.

4

I believe this is a time_zone issue, right ?