Not all user pseudo ID show up on Bigquery

[Apittha Unahalekhaka]

Hi All,

I am not sure if this is the right place to ask this question, but I really desperately need your help pointing to where the problem is. I am a graduate student that is doing research on usage pattern on a tablet app so we are using Google Analytics for Firebase and Bigquery. 

The problem: I know for sure that there should be 200++ users in a day in a particular city, but Bigquery only gave me 5 user pseudo IDs. This is a big issue for me, because I need to analyze the usage of each user.

Also, I realized that there is a very high mismatch between the number of users on Google Analytics for Firebase portal and the distinct count of user pseudo ID on bigquery. For example, GA would show me 80,000 users in the US in a day, Bigquery would only count 5,000 pseudo IDs. 

I am really lost on where the rest of the IDs went. I read earlier posts on the discrepancies, which are around 5-10% off. The discrepancies that I found were huge, and I don't think it's a problem with users being offline when using the app. Further, I am not sure if the timezone difference would cause such big difference. 

Am I understanding something incorrectly? I would highly appreciate any of your suggestions. 

Thank you very much,

Apittha