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
In my case ethermine connects normally to eu2.ethermine.org but since monday returning more stale shares (> 30%). Can it be a related problem related?