Could iOS download stats be wrong? Android counts right

Hi, I have deployed my first unity based app on Android (December) and iOS (February).

I'm sending install count and user statistics on my server. And here is the strange thing:

On Android Google Console the number of downloads is the same as in my DBS - that is roughly 6.5K, but the numbers differ for Apple.

On iTunesConnect I have like 1.5K downloads. However, my DBS counts 7.5K.

Alright, I have put the question in a way that you will say "Apple is not wrong, just your code has errors". Fair enough, I would like to know, what is making the difference seeing that Android works fine (same unity code used).

I was checking if it does not count only some "empty" installs - so here are other stats: out of 7.5K, 6.3K has at least one user. 5.8K of those users played at least 10 minutes, 4.7K played at least 30 minutes and 3.3K played at least an hour (it is game for preschool kids, no higher time lengths are expected).

Some "empty" installs were probably added in App Review process.. but what about those "real", where someone played?

My final thought is that maybe on some devices the storage is cleaned somehow and that leads in asking for a new id when played again. But I will gladly hear your opinion, if you have encountered similar behaviour.

Thank you