Hello,
Thank you for contacting Rank Math and sorry for any inconvenience that might have been caused due to that.
This is likely as a result of conflict with one of your installed plugins or theme. Would you mind helping us check if this is the case before we login by performing the tests outlined on this page: https://community.mythemeshop.com/tutorials/article/52-confirming-a-plugin-conflict/
We will be happy to take it from there.
Looking forward to helping you. Thank you.