I think I have found two bugs in gmail (by seeing its unwanted behavior)
1. This one has happened for years, now, solves itself in few hours. YOU CLICK on the email and it will not open. All other actions such as browsing through the boxes and delete etc would be working. SO you just gotta be patient for a while.
2. This one is more scary. Perhaps happening for a few months now. Seems like there is a bug that scatters the emails randomly and in large numbers (perhaps the ones it think are mass-notifications, it can drag some of your important message there if the message source is routine, that is your job-website or your bank emails) .
What happens? You can’t see a large number of emails, these are invisible, so after you read this, take my trick and check how many would be sitting in your email never read by you. You can’t and bet ya’ haven’t seen tons of emails that have been sent to you, few very urgent emails. Likely.