This can be the result of a page save/publish not completing fully at some point in the past. The approval/version is entered into a workflow, but not immediately cleared from it once published. You don’t need to have workflows actually enabled. Behind the scenes, the same happens.
If you are happy looking at the database, check the Workflow tables and you you will be able to manually unravel the tables/entries that relate to your problem page.
Always make a database backup before messing with the database.
If you are not happy digging about in phpMyAdmin, there is a workflow clearing tool in my Extreme Clean addon. If you search through GitHub, there have also been some stand alone php scripts published that do similar.
Again make a backup first. There are no guarantees that clearing the workflows will resolve this particular instance.