Mail obsessed with an old message This is on IOS but it has happened on OS X in the past.

No matter how many messages I have received, read, or replied to, every time I open Mail, the same five-week-old message is selected, and I have to scroll a long way to get to the new ones.

Not earth-shaking, but I'd like to find a way to make it always go to the new messages like it used to.

I moved the message to another folder, which made the inbox not have any selected.  But that's probably temporary—last time this happened, Mail soon began stalking another message.
The mail database is probably messed up a little. You can often fix mailbox folder issues by rebuilding them. It's easy to do.

Open Mail.app and select the mailbox with the email in question. That's the MAILBOX not the message. From the Mailbox menu select "Rebuild" (at the bottom of the menu) and let Mail do its thing. Depending on the size of the mailbox this can take seconds or quite a bit longer. When it is done I usually quit mail and re-launch. Not sure of that is strictly necessary though.