Can't see unread e-mails

Hi, Hi Hi Hello, wondering if you can help. I've had two problems recently, and not sure if they're connected: 1. An e-mail came into my inbox the other day and I briefly clicked on it but then must have knocked something because I saw some kind of warning message saying I won't be able to see replies to that e-mail. The e-mail (and warning message) then disappeared, so I asked other colleagues in that e-mail trail to re-send the e-mail to me. All three of them re-sent it but I never received it (and I don't think they got an error message to say it wasn't delivered). All other e-mails seem to be coming through fine. 2. Today my inbox is showing (4) in bold brackets as though I have 4 unopened e-mails. However when I scroll up and down the whole inbox I can't see any e-mails that are unopened. So I'm wondering if perhaps the initial e-mail I "lost" plus my colleagues attempts to forward this e-mail are "hidden" in the system somewhere? Any insight appreciated, thanks! Paula