Second eEmail being deleted from inbox when deleting one

Sometimes when I delete an email from my inbox it deletes another email. I then cannot find the second email in trash or anywhere. Seems to have started doing this in the last 2-3 weeks only. Sometimes when I delete an email in my inbox, it switches places in the list with another email, then when I try to delete it again 2 emails are deleted and not visible in Trash. Very frustrating.