Have you made any recent theme changes to your site?
If you use WordPress CMS, I would recommend setting up placeholders via the Ezoic WordPress plugin.
The plugin will generate placeholders for you and create an optimal layout across your whole site. This also means they're hardcoded if you'd like to change your theme in the future without impacting your site's revenue performance.
We've had new and existing publishers use it with great results, leading to higher EPMV and better earnings in a shorter timescale.
Here is an article that walks you through the process:
Setting up Ad Tester placeholders with the Ezoic Wordpress Plugin