Hello,
I apologize for the inconvenience you are facing with the Rank Math plugin on some of your pages. The issue you are experiencing where the plugin is not working on specific pages, like the one at https://rankmath.com/wp-content/uploads/2021/02/meta-box.jpg could be due to the homepage being set to display a specific page. In such cases, the Titles & Meta settings for the homepage can only be configured directly through the Rank Math MetaBox available in the Editor.
If you need further assistance or have any other questions, I recommend reaching out to the Rank Math support team by opening a support ticket at Rank Math Support. They will be able to provide you with more specific guidance based on your website’s configuration.
Thank you for bringing this concern to our attention.
Sources:
Fatal Error Happening on Some Installations After 1.0.49 Update » Rank Math
General Tab in Meta Box of Rank Math SEO Plugin
Understanding Rank Math’s Meta Box Appearing in Single Posts & Pages
Hello,
Thank you for contacting us and sorry for any inconvenience that might have been caused due to that.
Could you please confirm if the Rank Math SEO Meta box is not appearing on your About page? If so, please head over to your WordPress Dashboard > Rank Math > Titles & Meta > Pages/Posts and ensure that the Add SEO Controls option is enabled.

If you don’t see that option, ensure that you have enabled advanced mode to see the option.
In case, you’re using the classic editor then please expand the “Screen Options” and ensure that “Rank Math SEO” is checked:

You can follow this URL for more details on this issue: https://rankmath.com/kb/why-rank-math-meta-box-is-not-showing/
Let us know how it goes. Looking forward to helping you.
Thank you.
Hi there,
I happened to clear the caches, and now I can see the rank math option on my pages again. Thank you!
Hello,
Glad that everything has been sorted out.
Please feel free to reach out to us again in case you need any other assistance.
We are here to help.
Thank you.