Whenever you can't connect from outside the network it's usually one of 2 causes. In rare instances the redirection service at subsonic.org may be offline which causes the vanity addresses to fail. The message you got in your second post makes it sound like that may have been what happened.
More often, your server may have been given a new internal ip by your DHCP or you may have been given a new external ip by your isp and the subsonic.org redirector hasn't been updated yet.
The normal procedure would be to go into Settings/Network in Subsonic and hit the Save button. That will re-transmit your external ip address and the subsonic port number you use to the redirection service.
If that doesn't fix it, go to
http://canyouseeme.org and validate that the port is open and responding. If it is then the problem is at Subsonic.org, if not then your ip(s) have probably changed and you need to reset the port forwarding.
* - and please - don't post that "the port forwarding is fine" rather tell us whether or not it's been tested at canyouseeme.org and what the results were.