Rebranded URL loses certification

JotForm syntax:

https://form.jotform.com/account_name/formIDnumber

ReBranded syntax that prompts a security warning:

https://forms-account_name.office_domain.com/account_name/description

ReBranded syntax that works without the security warning:

http://forms-account_name.office_domain.com/account_name/description

Why doesn't the JotForm certification work for rebranded URLs create with a CNAME to use our office domain?

That may be happening since HTTPS is not supported with custom domains, so it would not be possible to link the form to a domain under HTTPS.