Describe the bug
When analyzing data from the Kenya research study, we found discrepancies between the data that was supposed to be logged from the phone and the data received in Firebase. In particular, data was completely missing for some stretches of time. We suspect that some events are being lost.

From further analysis (by comparing data received from Firebase to data logged on the apps), I estimate the event loss rate to be about 17%. This means that 1 in 6 events, on average, are being lost. However, note that, based on the data we have:

• The loss happens for stretches of events (not interspersed random events). I.e. lost events tend to happen in contiguous batches.
• The event recorded immediately prior to loss happens shortly before the first event in the 'lost batch', but the event recorded immediately after loss often happens quite a long time after the 'lost batch'. This suggests that perhaps the "not finished last batch" is not being sent.
• In addition to "last parts of batches aren't sent", I also saw some cases where entire batches were not sent.
• There is at least one instance, however, where the event recorded immediately after loss happens 4 seconds after the last event that was lost. Interestingly, the lost events are all of the same type (open/close revision card). Here is the relevant segment (timestamps in seconds):
  • 314: submit_answer_context
  • 314: end_card_context
  • 315: start_card_context
  • 339: submit_answer_context
  • 357: exit_exploration_context
  • 364: open_revision_tab
  • Lost events start here
  • 368: open_revision_card
  • 370: close_revision_card
  • 372: open_revision_card
  • 381: open_revision_card
  • 387: open_revision_card
  • 392: open_revision_card
  • 398: open_revision_card
  • 401: open_revision_card
  • 402: close_revision_card
  • Lost events end here
  • 406: open_lessons_tab
  • 407: open_revision_tab
  • 411: open_lessons_tab

To Reproduce
Unfortunately, we don't have clear reproduction steps. The phone were connected to the Internet for a few hours each day, but were mostly offline.

Expected behavior
All events sent by the phone should be recorded in Firebase.

Environment

• App version (you can get this through system app settings or via the admin controls menu in-app): 0.10-alpha_kenya-31b05b1e78