I don't know if you are hitting a bad cached version or hitting a bum re-direct, but the trigger is definitely "the Remote trigger". From the page you linked to:
...and there's no way to set a port.
@Hydro -- Peter is probably using port 443, maybe 80, as is usual for web APIs -- mainly because it avoids any problems with most firewalls. I'll try and check later, but you should check your own firewall logs.
Edit to add:
Yep, just remoted into work and set up a logging session against my machine there and:
...and if you reverse lookup that IP you'll see it's trigger.keyboardmaestro.com
So port 443 (HTTPS) indeed.
End edit
What's more likely is that the firewall -- or, if your "no firewall" is a different location to your "with firewall", some other piece of network equipment -- isn't maintaining the "long poll" connection. Some firewalls and routers can be rather aggressive at killing connections they think are no longer in use. See this thread for more.