As Admin:

1. Go to portal
2. Opt-in new help center from customize portal side panel

Repro-1, existing customer forget password flow:

1. As a existing customer
2. Go to portal login page and choose forget password
3. Follow links from the reset password email and reset password
4. Create a request after reset password succeed by click any project

Repro-2, new customer sign-up flow:

1. As admin, enable public signup for servicedesk from Jira Service Desk configuration page "/secure/admin/SDConfiguration.jspa"
2. As customer, go to portal and click sign up
3. Finish sign up by following sign up link from email
4. Create a request by click any project after successfully set password 

Both scenarios will fail with with error message "The security token was missing or invalid. Try refreshing the page", refresh the page can fix the problem.

This is not happening when opt-out portal X