Going to go ahead and ask all the obligatory network related questions so that if/when a dev notices this topic they might actually provide direct help faster rather than asking these same questions:

1. Are you using a physical ethernet cable to your computer? As in not using Wi-FI, Moca, or powerline networking solutions.

2. Are you running a single NAT network configuration?
Background information: NAT is a means for a modem and router to map IP addresses to the computers on a network and if two are running at a time it can be disruptive to network connections. If you have both a modem and a router only one of them should ideally have NAT enabled.

3. Do you have the ESO ports triggered or forwarded in your modem, router, and firewall?
These ports are: TCP/UDP 24100-24131, TCP/UDP 24500-24507, and TCP/UDP 24300-24331. They should be forwarded/triggered/allowed in every device that has a firewall between your modem and computer e.g.: modem, router, computer.

4. Are you running bandwidth intensive P2P applications like torrents while playing?

If your answers to these questions are: Yes, Yes, Yes, and No then hopefully a tech support can narrow down other possible culprits in the thread.