Hi,
Have tried rebooting the router? Can you reach its WebUI? If so, could you send me a Troubleshoot file via private message? It can be downloaded from the System → Administration → Troubleshoot page.
This a random guess and a long shot, but filled SMS message storage could cause similar behavior. Can you check whether there's free message space? You can do it in the Services → SMS Utilities → SMS Management → Storage page.