title: * Active Users Discrepency in Firebase/BigQuery*
body: <p>I have came across a problem in bigQuery and it's not making sense to me how is this possible. So scenario here is that we are upgrading/releasing our app to newer version and seeing how many active users we have on the newest/latest version that we released. I'm measuring this number (Unique Active users) using 'user_engagement' event (Definition of AUs from Firebase). Now here comes the problem. This number 'Active Users' should be equal to Number of Users (Who installed the app of latest version + People who upgraded the app to latest version). But there is huge difference between stats from these 2 sources.</p>
  
  <p>The unique number of users' that I'm getting via 'user_engagement' is far greater than that of from (first_open and app_update)
  Number difference is in thousands</p>
  
  <p><strong>First Query</strong>
  </p>
  
  <pre class="lang-sql prettyprint-override"><code>SELECT 
    count(distinct user_pseudo_id) as new_users_on_app_version 
  FROM TABLE 
  where event_name IN ('first_open','app_update') 
    AND app_info.version = '5.8.1' 
    AND _TABLE_SUFFIX BETWEEN '20190515' AND '20190527' 
  </code></pre>
  
  <p><strong>Second Query</strong></p>
  
  <pre class="lang-sql prettyprint-override"><code>SELECT 
    count(distinct user_pseudo_id) as active_users_on_app_version 
  FROM TABLE 
  where event_name = 'user_engagement' 
    AND app_info.version = '5.8.1' 
    AND _TABLE_SUFFIX BETWEEN '20190515' AND '20190527' 
    ##Note: 20190515 is the data when we released the new version 5.8.1 
  </code></pre>