Thanks for reaching out.
It sounds to be that portfolio type is inactive or removed but i couldn't confirm it through the site's front. Would you mind providing your site's admin login credentials in the secure note?
There is no child theme either so I assume this can be caused by plugin, so for the meantime, you could try testing for a plugin conflict. You can do this by deactivating all third party plugins, and seeing if the problem remains. If it's fixed, you'll know a plugin caused the problem, and you can narrow down which one by reactivating them one at a time.
Let us know how it goes!