Firebase events demographics

We are using Firebase to retrieve the interaction of users with one our app. It works fine but we are currently trying to understand how Event demographics are reported.

We found here that event demographics are reported only if a threshold is reach, here we found that this threshold is "at least 10 users per age/gender bracket" (we could not find this information in Firebase documentation).

We made several tests on more than 10 devices and as you can see on the screenshot below 25 Users are reported but we still don´t have event demographics.

enter image description here

If 25 users used our app, how can it be that we do not have any event demographics? It is unlikely that they all fall in a different bracket. Can it be that the 25 users reported by Firebase correspond to app instances while Firebase needs 25 different google accounts to report events demographics ?