standard/input/FormSubmit on_success_url is redirecting to AAQ rather than the on_success_url

Summary

Application form that creates a contact based on email address

Content

I have a form that captures customer information through a membership application where most fields are required in order to apply. On submit, the page should redirect to a *_confirm page that provides a message and ref number. When applying using an existing contact (based on their email address), the form works fine.

The issue is when someone applies while creating a new contact record. The on_success_url seems to be ignored and the user is directed to the "ask a question" page instead.

We are currently using 20C and standard/input/FormSubmit ver. 1.5 (the latest is 1.6 but doesn't seem like it will fix anything related to this issue).