Hello @lryo,
In this case, while saving the metadata, please keep the browser console open in the “Network” tab and see what the status code of the following route: https://www.yourdomain.com/wp-json/rankmath/v1/updateMeta?_locale=user
You can find the browser console in your browser following this guide: https://balsamiq.com/support/faqs/browserconsole/
If it’s returning any other value than a 200, there’s something wrong with the route and we would request you to get in touch with your hosting provider to make sure that REST APIs are not getting blocked.
However, if it returns 200 status code, then you can try to follow this guideline to check if any of your plugins/themes are conflicting with Rank Math: https://rankmath.com/kb/check-plugin-conflicts/
Regarding the discrepancy in SEO score, please head over to your WordPress Dashboard > Rank Math > Status & Tools > Database Tools, and from there click on the button “Recalculate Score”, and wait for it to process and see if that helps to resolve the issue: https://rankmath.com/kb/rank-math-status-and-tools/#recalculate-seo-score-for-posts
Let us know how it goes. Looking forward to helping you.