X_ProxyServerRedundancy will (hopefully) cause the OBi to try another one of Anveo's PoPs, should this issue recur. (They have several.) If my guess is correct, this will have the same effect as changing the port number (new NAT mapping will be created), but it will happen automatically without you having to change settings.
You've probably already checked this, but just in case, make sure your E3000 receives a public IP address from your ISP. If your modem is also acting as a router, you have a "double NAT" situation which makes this problem much more tricky to troubleshoot. In this case, I would place the modem in bridge mode and let the E3000 do the LAN routing.
Alternate solutions which might work:
1) Increase your OBi's RegisterRetryInterval so that your router's corrupted NAT connection expires, and a new one can be created. A quick Google search for "cisco e3000 udp timeout" did not produce any relevant results, so the number to use will be a guessing game. If the problem comes back, you could try to unplug the network cable from your OBi for five minutes, then plug it back in. If it doesn't register, then try to unplug the network cable for ten minutes. Keep going up in increments of five minutes. If for example it registers after being unplugged for fifteen minutes, you can set RegisterRetryInterval to 960.
2) Your router is compatible with
Tomato firmware which does not have this issue (any more). So, if you don't get things working with the stock Linksys firmware, that is an option. If you do this, let me know so I can give you some pointers about configuring timeouts.
