Are you a dedicated Gmail user? Did the important email from your coworker never show up in your inbox? It and many other unexpected emails may be incorrectly placed in Trash, Spam, or other misleading folders. An issue in Gmail was caused when a bug was found in a Gmail software update on January 15th. The issue was fixed on January 21st, so the week in between dates is when the damage occurred. Actions such as deleting, reporting spam, starring, archiving, or moving to a folder, were incorrectly applied to a different message than the user implied. The affected users were those accessing Gmail from the Gmail Application in iOS, a mobile browser, and Gmail Offline. By January 21st the Gmail engineers identified affected users and notified them of the issue. They also provided a list of users whose messages may have been misfiled during the week. Gmail is sincerely apologetic and has assured users they have performed an internal review and are in the process of implementing to help prevent a recurrence. WSD's advice is to check your Spam and Trash folders for the dates above. Do so quickly as spam and Trash folders are automatically permanently deleted after 30 days. Also, check your inbox for the dates as well to make sure no messages intended for Trash or Spam are still hanging in your omnipotent inbox.
Google App Misfiled Messages