I've seen something similar occur before a few times. We have usually traced it to the ISP's modem, funny you mention the auto updating as that was the route of a few of our issues as well. When the issue occurs, can you access the wired.meraki.com page, does the MX report connection to the cloud? You can ping the Comcast modem as well, but you can't go any further? What does a trace route out show? Can you try pinging google.com and then 8.8.8.8 to rule out any form of DNS problems. Is there anyway of getting a device in there to do a packet capture and find out what is going on?
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