There is a known problem with many devices. It has to do with the renewal of the DHCP license (typically, every day). Many of the industrial routers handle the renewal via the line cards rather than the router's main processor. However, that code is new and was designed according to some updated standards ... in particular, the size of the packet (old DHCP used a fixed, minimum, packet size). A lot of "leaf" (end of line) devices reject DHCP messages sent over short (newer) packets do not conform. So, when the new line card software sends the "new" format DHCP renewal, the device (the router) ignores it.
The work-around, so far, is to power cycle the leaf MoDem/router combo. That forces the (more capable) software in the back office router into play and the renewal becomes a new connection.
Pain in the butt? Yes! It looks like some kind of fix will have to be applied to the Cisco and Juniper hardware (I think Juniper already has the fix deployed) to compensate because the various ISPs aren't going to spring for upgraded leaf equipment for everybody.
Is this the cause of this, reported problem? I don't know, but it sure sounds similar to the problem that Verizon had a short while ago.