Dear Amplitude Community,

Faced a problem with segmenting events using the "group by" grouping tool combined with unique events.

I will describe the situation in more detail.

Step 1: I have a task to calculate the conversion rate using a simple click/visit formula. I select a custom event in Event A, which includes the necessary events labeled as "click", and in Event B - custom events "visit". Then I write the formula %:UNIQUES(A)/UNIQUES(B). For example, let the value be 60% for date X. 

Step 2. In each event, I set "group by" on the event property that overlaps in events A and B. Amplitude correctly calculates % for each value of the property.

Step 3: I remove the formula from the calculation and use CSV export to download the clicks and visits data for each value of the property within which the grouping took place and load the data into Excel. Then I sum up all clicks and all visits and use the formula sum(cilcks)/sum(visits). I expect to get a value of 60% as in step 1, but I get something completely different, let's say 50% for example.

Step 3: Trying to find out at which step the error occurs, I find out that the grouping needs to be corrected. For example, there are 1000 clicks on event A, which I see in Amplitude. When grouping by the property of event A, the sum of each of the grouped values is not 1000 clicks, is 1500 clicks for example. How is it possible?

Please, help to solve this problem. Where to dig further?

P.S. This problem occurred recently before the calculation was performed correctly.