No servers listed is usually packet/routing issues. Sometimes you can try logging in a few times until they appear. If you are on wifi, you can try a wired connection and see if its more stable. Many are just temporary if its a hub that traffic is going through thats having an issue. If available you can try a VPN or tether/hotspot to reroute traffic and see if it helps.
You can also try the Middlemand login helper that reduces the amount of data trying to be processed and will only focus on the p99 servers
https://github.com/rm-you/p99-login-middlemand/releases