Emails disappear after I click on them. They do not appear in my Trash folder. I've lost several important ones.

I just posted about the same problem yesterday that's recently been happening for a couple of weeks now.  Here's what I did find which I also mentioned in my post yesterday.  If you do a search of your "Inbox" for either the Subject or Sender of that particular email that you just opened and just disappeared, it will find it.  It's still there somewhere but it's not in the trash or spam.  I just can't figure out why or where it did go but by doing that search it will find it.  You just have to be super aware of the Subject or Sender before you open it especially if it's an important email.  Sometimes it disappears as soon as I click on it and sometimes it disappears after I return to the Inbox.  It's a real hassle and I am still waiting for a response as to why this is suddenly happening to random, unrelated emails and not to every email I open.  Hope this helps a little!