After receiving my replacement cable modem from Motorola Arris I went through the process of setting it up with Comcast. Only a week later the new modem suffered from the same problem as the old one. This was frustrating because it meant that the problem I suffered was likely a design flaw instead of a manufacturing error. It also meant I did not manage to find the root cause.
After resetting the modem I decided to take another swing at Googling my issue. This time my Googling was better and I find a thread on Broadband Reports describing similar symptoms to mine. A large number of folks on this forum suggested that the issue was the upload being saturated on the modem causes it to crash. The recommended fix was to go into my router settings and to set a limit on upload going from the router to the modem.
Sure enough this fix appears to have worked, at least so far. I set an upload maximum equal to Comcast’s stated service level speed (they usually provision the upload at a bit faster than that) and have been running my modem without issues for about a week now. If this works and was truly the cause it is frustrating for multiple reasons. First is that given the wisdom of the crowd on the forum, it is likely that Motorola Arris knows about this issue. Yet they did not mention it as a possibility. Second if they did not know about the issue it is disappointing that such a large company lacked awareness of the problem that appeared pervasive enough to generate online conversation. Surely they could do better by their customers.