Recently I noticed that my GMail inbox showed ‘0’ unread emails but my Android phone showed ‘1’ unread email persistently. I found the following trick which solved this problem. On my handset I clicked on ‘Search’ option and then typed the following in the search bar:
This allowed me to show only unread email in my Android Gmail client. Out Popped a one and half month old email which was still unread. All I had to do was open that email and the issue was gone.
What is not clear to me is how the GMail website showed 0 unread email while the Android client showed 1 unread email simultaneously for weeks at stretch. Perhaps the Android GMail client does a better job at keeping track if you missed reading a particular email a while back.