I have the same issue. And posted in another thread (here) about it with screenshots. So far I have not found a solution. SSL is set up and working (tested).
So far I have not found a solution - was it indeed just a bit of time and it startef working?
@RSimmons-Well when I try Chrome mobile, I see the site. When I try Safari or Firefox mobile, it says the page is unavailable and that the connection is not secure. Are you sure the SSL is correctly set up? I'd start there in your domain registrar, then work with HubSpot to ensure the subdomain is correctly set up as well.
Did my answer help? Please "mark as a solution" to help others find answers. Plus I really appreciate it!
Based on the tests I've done, I can see that this issue only seems to be happening when trying to load the wesbite through Safari. When I try with Chrome or Safari, I can access the website just fine. This leads me to believe that the problem is coming from Safari and not HubSpot.