Hello,
Thank you for contacting Rank Math and sorry for any inconvenience that might have been caused due to that.
This error suggests that there is some custom code on your current theme that is referencing some Rank Math functions. Please ensure that you have Rank Math activated on your site and if you are not using our plugin, please comment out the function my_custom_RM_title_replace_vars from your theme.
Looking forward to helping 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.