Hello,
Thank you for contacting Rank Math, and sorry for any inconvenience caused.
Rank Math shows the Primary Taxonomy category in the Breadcrumbs. Can you please confirm, if that is set in the Titles & Meta Settings of Page/Post: https://rankmath.com/kb/titles-and-meta/#primary-taxonomy

I hope this helps. Looking forward to helping you.
Hello,
We are super happy that your issue is resolved. If you have any other questions in the future, know that we are here to help you.
If you don’t mind me asking, could you please leave us a review (if you haven’t already) on https://wordpress.org/support/plugin/seo-by-rank-math/reviews/#new-post about your overall experience with Rank Math? We appreciate your time and patience.
If you do have another question in the future, please feel free to create a new forum topic, and it will be our pleasure to assist you again.
Thank you.