Hi there,
Unfortunately a lot of people will go with the “theme related” or “plugin related” answer when they’re stumped.
I’ve never heard of this happening. If the page is viewable, and has an ID (which it does), then it has to be in the database. If it’s in the database, it has to display in the Dashboard, as it checks the same database as the front end.
If for some reason something became corrupt, you may need to delete the page through the actual database.
This is the page ID: 3524
Might be worth asking your hosting support to do it if you’re not familiar with PHPMyAdmin.