Are you running a page or post builder?
We recently made a change to our Mediavine Control Panel plugin to prevent ads from being loaded in the editing interface of post builders such as Thrive Architect, Divi Builder, WP Bakery, Elementor, and Live Composer. This was causing issues, such as broken ad code being added into posts in some cases. The change prevents ads from appearing anytime you are logged into WordPress.
If you would like to test your ads, please log out of WordPress or check from another browser (where you also are NOT logged into WordPress). Also use an incognito or private browsing window and ?test=houseads at the end of the url to ensure you are seeing accurate results.