The signalling server's been running fine, I haven't noticed any problems. Its uptime is currently over 13 days, and we generally only have a minute or two's downtime once a month when "patch tuesday" comes around and Windows Update does its stuff. You should also check for signalling errors and display any that occur, since a common mistake is to accidentally flood the server by sending it stuff every tick, and then it kicks you for exceeding the flood limit.
Connectivity issues like this are basically standard no matter what technology you're using - antivirus, firewall, exotic router configurations, service outages, Internet traffic flow quirks, etc. etc. all means sometimes connections don't work properly. There's not currently any good way to identify the cause of problems. There's not much advice you can offer except telling users to check their firewalls and internet connection.