title: Firebase Crashlytics on Android not persisting user id across app restarts
body: <p>In our app we call <code>Firebase.crashlytics.setUserId(identifier)</code> when a user logs in and  <code>Firebase.crashlytics.setUserId(&quot;&quot;)</code> when a user logs out.</p>
  <p>This means such methods won't be called across app restarts.
  The rationale for this is based on my (possibly wrong) understanding, by briefly looking at the <a href="https://github.com/firebase/firebase-android-sdk/blob/976ea2fb443bbf7b5828f988275110b6b3b4b281/firebase-crashlytics/src/main/java/com/google/firebase/crashlytics/internal/common/CrashlyticsController.java#L421" rel="nofollow noreferrer">code</a> , that the SDK is persisting such information to disk.</p>
  <p>However I've now noticed that only crash reports that come right after a user has logged in have a user id attached. Whilst any other crash reports that happen after application restarts does not have any user id attached.</p>
  <p>Is this a bug?
  Is the SDK actually persisting the user id value?
  Should I call <code>Firebase.crashlytics.setUserId(identifier)</code> on every app startup (e.g. in <code>Application.onCreate()</code> ?).</p>
  <p>Is there some additional debug I can do?</p>