iPad Mail always highlights an old message on launch

Whenever I launch Mail on my iPad and select a mailbox, Mail always highlights the same old message from a week or more ago and to get to the latest messages, I have to scroll through hundreds of messages to get to the top. If I delete the highlighted message, Mail seems to simply latch onto another message to highlight on launch.

I realise that this is a minor problem but it is very annoying that even when I have unread messages, Mail does not itself highlight the most recent message.

Does anybody have a tip to fix this, please?