Backtracking on breadcrumbs does not work in the Service Portal
This issue can be caused because the field called Catalog category home page on the portal record is supposed to be empty or point to the categories page. Instead, in this case, this was pointing to the sc_cat_item page. This value is used in the widgets when setting the breadcrumbs URL values. The system tries to get the value from this field or it defaults to sc_category. Since it was set to sc_cat_item, the system tries to open a catalog item with a sys_id of a category which resulted in the breadcrumb navigation not working.
To resolve the issue, either empty out the value for the field, Catalog Category Home page or point it to the catalog categories page that you intend to use in your portal.