Hello,
Thank you for contacting Rank Math, and sorry for any inconvenience caused.
Assuming you are using the latest version of all the plugins and the themes (please update if not yet), this seems like a cache issue. Could you try using a different browser (Chrome preferred) and try a hard refresh to clear the cache JS and CSS file with the page in question opened?
Windows: Ctrl + F5
Mac/Apple: Apple + R or command + R
Linux: F5
Here is a detailed article on why your focus keywords are not saving.
https://rankmath.com/kb/meta-data-not-saving/
We really look forward to helping 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.