Not all emails in list are selectable

When an email arrives, it is visible in the list of emails. However, some of them are not selectable. For example, in the attached screenshot (thunderbird.jpg), you will see that an email from Newegg.com is selected but the viewing window shows Mutual Of Omaha (probably a scam) and does not allow me to view the Newegg email. Additionally, as I look through my emails from Newegg, the vast majority of them are selectable. However, I note that one in the list actually shows a different email in the text window. In this case, I click on a Newegg email from 9/21 but what shows in the viewing window is an email from WebhostFace support (thunderbird-02.jpg) To the best of my lknowledge these problems have only started to appear in the last month or so. Thanks, Dave Davis