C6220 reboot daily

For over a week now, I've had to reboot my C6220 cable modem/router at least once per day.  Now, we are gone all day during the week, but I have to reboot every night.  It's getting really old and my husband is super frustrated as to why this modem/router that we've had for all of 6 months is doing this.  Please help!  I didn't change anything when I set it up.  I just plugged everything in, called my ISP and had them change it on their end.

Thanks!