Limit post navigation to category

Hi Jason

Thanks for reaching out 🙂

Please, try the following child theme:

https://purothemes.com/wp-content/uploads/2016/02/ultra-child-post-nav-in-same-term.zip

To install:

1. Download the ZIP file to your desktop.
2. Go to Appearance > Themes > Add New: Upload Theme > Activate.

Activating a child theme in WordPress will cause menu location settings and Customizer settings to reset. Unfortunately, these will need to be reapplied if you want to make use of the child theme.

Give it a try and let me know how it goes.