Did you know, by default client callable script includes do not run on portal for external users with snc_external roles.

To sort out this, create an ACL of type client_callable_script_include for your script include and add ‘snc_external’ role to Requires role list.

More details can be found here: https://support.servicenow.com/kb?id=kb%5Farticle%5Fview&sysparm%5Farticle=KB0749222