I have the same isues and I think that is a DNS problem, but I can not check it because I'm on private network that can not change the DNS , I make a proxy outside this network and I connected the proxy to the pool and now it's fine
It was not a DNS problem.
I had a machine that could ping eu2.ethermine.org, I got the pool's IP and tried to ping it (no domain, the IP) from a mining rig and still no ping.
As I said, in my case the problem got resolved on its own. Must be some European ISP route or something