It looks like some users who have Gmail on their Windows Phone 8 devices are experiencing syncing issues that eventually cause the email app to crash. The problem seems independent of hardware (so 8X and 920 users are affected) and is tied to Gmail specifically.
The problem occurs with the People Hub and linked contacts constantly syncing. Likewise, when people head to their Gmail inbox, it too is stuck on a constant sync and may even crash when one attempts to scroll the message list. Over in our forums, user moc426 made the above video of the phenomenon occurring, a test which site WinSource has also validated as happening on their HTC 8X.