Gateway Site Flagged as Malicious

I have a gateway hosted on a site domain. I am having issues where certain security measures (Fortinet, ISP providers, etc.) are flagging the site as unsafe. A couple theories are that they are flagging code that's running on the web page or that it might be because it is a newly setup site. However, we have dev and staging sites that are functionally identical that are not having this issue.

Has anyone ever encountered a similar issue with other gateway sites or have any ideas on what could be flagging these security measures? Any thoughts on how to better identify the issue?

In my experience, Fortinet just uses a random number generator to determine if it's going to flag a site or not...