I'm a techie type and have one of those comcast modems. I also have a descent Ubiquiti setup that rides behind it, but I'm kind of shoehorned into using their provided modem or alternatively paying for a modem myself and then paying another $35/month for "unlimited data" (Really crappy comcast policy but that's beside the point).

Long story short, this modem will reset itself and require me to not only become aware that it's once again broadcasting the "xfinitywifi" hotspot, but to also redownload the xfinity app, configure the app with my information and try to remember where they buried the setting to disable this "feature". After disabling it somehow takes up to 24 hours to actually happen....