The LOS steady or blinking red light indicates any of the following reasons below. Fiber cable bend (from NAP box or pole going to your modem). But here's what I want you to know right off the bat: this isn't some mysterious technical nightmare that needs a genius to solve. I've fixed dozens of these, and I'm. A LOS red light in your router or modem means that there is a disruption in the fiber optic connection from your Internet service provider (ISP), hence a “loss of signal” (LOS). Had to scroll to far to find someone who actually knew what LOS meant. In this situation, you do not have to interact with the configuration of the computer or the.