I had the same issue a few months ago due to not having enough ports forwarded. I can't imagine though you've changed anything to make the sever not show up, but check these lists below just to be sure (assuming your server is hosted via router and not an online paid server).
Make sure your server device's IP address is still "Reserved" and not DCHP. Make sure your Reserved address is still applied in all the ports. Port Management: Disable all rules and allow inbound traffic through (may be optional).
Check via a website (whatismyip) or "ipconfig" in command prompt to verify that your server's public IP address didn't randomly and mysteriously change addresses.
Lastly I suppose checking the server.cfg again, make sure "seta dedicated 2" and not "1", "seta net_port 12203", and remove the "seta net_ip" if it's there (I didn't need it for the server to work).
Code:
TCP: 18020, 28900, 28910, 29900-29901, 29920, 5900
UDP: 12201-12202, 13139, 27900, 29910, 3783, 6500, 6515
TCP/UDP: 12203-12218, 12300, 6667