Any loose IPS connection cables, internal ethernet cables, or power supply connections?
Are you able to view and inspect any exterior connections coming into your residence?
Any signs of overheating in the cable modem or router? What cable modem are your using? Is it yours or ISP?
Have you contacted your ISP?
My thought is that it is a bad connection local to you. But whether that is on the ISP side or your side is TBD.