Their crappy equipment needing rebooting every few weeks, not ridiculous. Their purchasing gear from incompetent vendors who cannot be standards compliant for PoE PD negotiation, tragically plausible.
Many customers buy their own cable modem. You can lease an Xfinity device as well and those function pretty nicely these days but YMMV. But typically a device reboot is a way to quickly solve a few different kinds of problems, which is why techs will often recommend it as an initial step (you can generally assume that there's data behind what occurs when any one of tens of thousands of support reps suggesting something to a customer - support at scale is data-driven).
He's got graphs showing it every 24 hours? Liar, liar, pants on fire, lazy SOB is looking for an excuse to clear you off the line.
Could well be from noise ingress - lots of work goes into finding & fixing ingress issues. Hard to say unless we look in detail at the connection in question and the neighborhood node. JL