I would try this, disconnect the Ethernet cable from the one Hopper it's connected to and on Both Hoppers, go to your Internet Settings (Home x3, #2 - Networking, then #7 - Internet Settings - I may have named those wrong, but those are the numbers) then on the remote, hit Info and then Recall and say yes to clearing internet settings, do a reset network and reboot. that's starting from scratch.
Making sure Bridging is on, on both Hoppers - which it should be, it is by default, connect the one to the Ethernet and use the Top LAN Input and it should connect then give you the Popup that it's sharing the Network. Once it's done, everything should be Moca Connected and the Hopper with the Ethernet should say Using Top Ethernet Port - WiFi Disconnected (or Disabled)