I've got the same problem. I've played previously without issue and now I simply can't connect to the server list. And it doesn't seem like it's a router or firewall issue on my end.
Edit: I found the solution:
https://github.com/Zaela/p99-login-middlemand it works for me using wine on linux at least, and it looks like it can be used on windows as well (but I'm 100% sure)