user measure google analytics

Facing the same issue and understanding how GA works, I can provide an answer but not a solution.

The fact is that a user is not a summable metric against the days dimension as "users" are actually "unique users". That's because Users on day 1 + Users on day 2 will NOT be equal to Users on day1+2, since there are some users that have been visiting our site on day 1 AND day 2.
So imagine that on day 1 you have users

A, B, C

and on day 2 you have users

C, D, E

GA tracks users with cookies so it's able to recognize that user C on day 2 was the same on day 1.
Unique Users Day 1 = 3 (A, B, C)

Unique Users Day 2 = 3 (C, D, E)

but Unique Users Day 1 and 2 = 5, not 6 (A, B, C, D, E)

When you run the report for a certain time period in GA, it will count only uniques on the time period, But when you connect PowerBI to the GA and you get the users metric against and the time dimension, it will report you 3 users on day 1 and 3 users on day 2, hence you sum them and makes 6 not 5.

What could be the solution? Keep in mind that I haven't tested yet:  downloading the user metric but choosing only the week or month dimension instead of the day, so (probably) GA provides the uniques for the week or month, which you can show in your report when the period is week or day. But you really can't count unique users like you do on GA on any time range UNLESS you download each and every occurence of a users with it's "client ID" (GA unique ID), which I don't think it's possible.