In a notice appearing for some Gmail users, Google confirmed this issue occurred between January 15 and 22 and is now fixed. It only affected users who accessed Gmail via the iOS app, a mobile browser, or offline in a desktop browser. Google advises users to check their spam folder and trash for emails that were marked incorrectly.
The issue is the second round of technical difficulties for Google's Gmail service in less than a week. Late last week, Google's cloud services went offline for approximately an hour. The Friday afternoon outage affected Gmail, Google Calendar, Google Talk, Google Drive, Google Groups and other services.