My dedicated server no longer shows up in the master list of games, but you can connect to it if you have the IP in your favorites. This is a dedicated server in a data center and I do not think that I am having a port forwarding issue. I've been using this host for 7+ years. I'm noticing that I can't ping the master servers that I know of and I also do not see the " Masterserver added xx.xxx.xxx.xx" feedback in the startup any longer.
$ ping hl1master.steampowered.com
(22.214.171.124) 56(84) bytes of data.
ping statistics ---
7 packets transmitted, 0 received, 100% packet loss, time 6000ms
valve@46:~$ ping 126.96.36.199
PING 188.8.131.52 (184.108.40.206) 56(84) bytes of data.
--- 220.127.116.11 ping statistics ---
4 packets transmitted, 0 received, 100% packet loss, time 2999ms