Yeah, I deleted it because I think what you're dealing with (trying to get a certificate on Fortigate) was actually different than the thread that I'd linked to (which was issues with Fortigate firewall SSL interception not liking sites that chained to the expired root). So I don't think my message was actually useful or correct, so I deleted it.
I'm not familiar with Fortigate myself, I was just trying to point related things together.