When you change your theme, placeholders may not all translate well across to your new theme, which has the potential to impact upon your revenue. I'd recommend reviewing your placeholder setup on your top landing pages with these top tips for optimizing your revenue: https://support.ezoic.com/kb/article/ezoic-ad-tester-best-practice-guide
If there are divs that are no longer available the Ezoic system may have automatically removed some placeholders so it's important that you add additional placeholders in to compensate. The article above has a link to a video on how to do that using our ad tester chrome extension.
If any placeholders have not translated well to the new pages we don't recommend deleting them if avoidable as these may be placeholders that are generating a lot of revenue, but instead, try adding padding and changing the sizes which are enabled so that no placeholders are overlapping and that you have at least 1 of every position type per page where there is the content to support it.
After you have made these changes, there may be some impact on revenue in the short term, as the system will need a little time to adapt to the new setup and collect new information about user behavior and adapt to optimize.
If you would like any assistance with this, please do feel free to reach out to the Support team.