Hmm the plot thickens. I have now noticed that in Filemaker 14 I can access the server via Filemaker Pro using the IP and the domain name, but with FM pro 15, it only works with the IP address. Could it be a problem with the SSL certificate? Do I need to install it again after the FM Server 15 upgrade?
As far as I know you do need to install your SSL cert again. Although I am not sure that is the problem. You should be able to connect with the default certificate. Have you tested disabling the OS X firewall to see if you have access? If you still have the same problem then it is not your firewall settings.
FMI offers free install/upgrade support for FMS. Worst case you can give them a call.
Are you trying to connect on the same LAN or over WAN? If WAN did your FMS machine reassign a new IP address? maybe the port settings need to be adjusted or you need to set the server to a manual IP address.
After rebooting the server twice, I can connect to the admin console remotely now. Another problem seems to have cropped up though. Filemaker 14 and 15 are not giving me any errors when I connect via IP address instead of domain name. It should give me a grey lock, but is giving me a green one no matter how I connect.
Not sure what to suggest. Rekeying your cert?