Hello,
Thank you for contacting Rank Math and sorry for any inconvenience that might have been caused due to that.
Mobile usability is commonly related to the design of your site. How are you creating your pages? Are you suing a page builder? You can check the issues related to your sites mobile usability by testing your URL with Google pagespeed insights or this external Tool.
You can also check this article that explains this further
Hope this helps you. Thank you.
Hello,
Since we did not hear back from you for 15 days, we are assuming that you found the solution. We are closing this support ticket.
If you still need assistance or any other help, please feel free to open a new support ticket, and we will be more than happy to assist.
Thank you.