Hello @aki_Z ,

There is an OOB Widget for the breadcrumbs for portal
Navigate to All > Service Portal > Widgets , search for widget : "breadcrumbs"

Please check if there are any modifications made to the OOB script in widget. If changes are found, revert it back to original OOB version and then verify if the issue is resolved.

If you find the solution helpful, Please mark as Helpful!
Thank you

Regards
Rohit