Cable internet through a DPC3825 and seemingly randomly it will completely drop it's connection to the internet and never get it back until I reboot it.
The gaps between drops have ranged from 10 minutes - 5 days but when it does drop, the US, DS, and Online lights on the front turn off and then I've got nothing over wifi or wired until I reboot it.
I can see it trying to get its connection back as those 3 lights will blink. The US and DS lights will usually turn solid before the modem dies again and the cycle of blinking lights starts over again.
I'd guess this is some problem with the actual modem hardware. I do have another router I could use if bridging would help.