Have you first tried power-cycling / re-starting the device ? No joy ? Try hard resetting the device to factory defaults by pressing and holding in the recessed reset button on the rear for 30 seconds. This can sometimes clear up some weird behavior issues. You will lose any customized settings, and they will need to be re-configured from scratch if you do the latter.
Sorry that didn't work. We've been seeing many posts about this issue here lately ! It may be a firmware glitch. I can only suggest that you try having it swapped out for a different make / model number gateway. Good luck !