LOS stands for Loss of Signal, and it refers to a problem with the signal reaching your device. LOS can occur when there is a problem with the fiber optic connection, such as loose cables and connectors, damaged cable or cable pins, or when the optic cable has been bent abnormally. The LOS indicator on a modem or router is usually a red LED that may be labeled "LOS" or "Internet". When LOS occurs, the modem or router cannot communicate with the internet service provider (ISP) due to signal loss, which means that you cannot access the online world.

To fix LOS, you can try the following:

• Check the cables and connectors to ensure they are properly connected and not damaged.
• Restart the modem or router.
• Wait for some time, as the problem may solve itself without your involvement.
• Check for bent or damaged pins on the router and try to restore them using tweezers or any other tool. However, this can be complex, and if the circuit board needs to be replaced, it is usually more expensive than buying a new router.
• Contact your ISP to check if there is an outage or any service disruption on their side. They can also test or restart your connection and assist you in fixing the problem.

Different modems provide different indications for when there is a loss of signal, so it is best to refer to the modems manual for specific instructions.