You might try configuring the public address settings:
Additionally, take a look at the Use Proxy Forwarded Headers option to further optimize your setup behind a reverse proxy (by having Ignition implicitly "trust" the headers set by your reverse proxy in order to reflect the true client IP address instead of that of the reverse proxy itself).
I configured the public address:
My SSL certificate is recorded on my gateway:
I registers it as trusted certificate on my designer, but when I add the https address of my gateway, I get this error message:
Last, my problem is still there.
When using SSL, your public address configured in Ignition must be something named in the certificate, or an IP address identified in the certificate as an alternate. Your configured public address does not match the screenshot of your certificate.