I have a RE450 extender that I use to extend the wireless access of my Dlink DIR-859.   For the most part it works as expected, however at least once every couple days, we find that our cell phones and laptops cannot access the internet and have to unplug the RE450 to restore service.

Oddly enough when this occurs, the devices still connect to the RE450, but don't seem to have any network access at all.  Via the browser I cannot access the RE450 or the Dlink(wirelessly).  Using a wifi analyzer I can see both the primary wifi signals and the extended signals at both frequencies.  On a wired connection in the house all is fine and everything looks good on the router.

The RE450 has a static IP on our network.  

So it seems that the RE450 continues to take connection from clients, however it loses connectivity to the primary signals.

Firmware is up to date