Do the clear the history thing. See if that helps.
I’ve cleaned my browser cache several times during this debacle.
The problem APPEARS to be exclusively limited to the Inbox Web page - as I can [usually} open “Recent Unread E-Mail” from the main Yahoo E-Mail Web page.
Also, I can right-click and copy the link shortcut of a given e-mail on the Inbox Web page, paste it into the URL box at the top of the browser, enter, and then get to the e-mail.