Hello @anndyi
Please check the following new screencast:
https://i.rankmath.com/cJOdLa
Everything is working fine when using the latest version of Rank Math & the Classic Editor.
As requested earlier, and assuming you are using the latest version of all the plugins, themes, and WordPress (please update if not yet), it would seem like a conflict with one of the plugins or the theme you are using.
To determine that, please follow this troubleshooting guide:
https://rankmath.com/kb/check-plugin-conflicts/
Only the site admin would know and your users won’t be affected by this troubleshooting.
Looking forward to helping you. Thank you.