Thank you for contacting Rank Math support, and sorry for any inconvenience that might have been caused due to that.
Can you please confirm if you are using the default variables to pick up the values from your actual post title? If so, please check if the correct SEO title is showing on the snippet preview. Please refer to the example screenshot below:
We have tested this on our end and we can’t seem to experience a similar issue as yours.
Assuming you are using the latest version of all the plugins and the themes (please update if not yet), it would seem like a conflict with one of the plugins or the theme you are using.