Thank you for posting your question to the Slingbox Community. From the information you've provided, it sounds to me like it could be one of two potential causes. The most likely culprit is something called HDCP. HDCP stands for High Bandwidth Digital Copyright Protection, and is a form of content protection utilized by many of today's television channels. Basically, what this means is that often times, a channel's video signal will be disrupted if there is an HDMI cable involved in your cable configuration. This impacts Slingbox users who have their M1 configured with either component or composite cables from their cable box, while simultaneously having their cable box connected directly to their TV using an HDMI cable. If this sounds like how you have your Slingbox arranged in your home, try removing the HDMI cable from the situation. If you want video signal to your TV without using the HDMI, I would suggest using the pass-through option by connecting either component or composite cables from the outputs on the Slingbox to your television set. When setting up a pass-through, just ensure you are using the same type of cables going from your cable box to your Slingbox as you are using from your Slingbox to the TV.
The second, and less likely, potential cause for your issue could be that your Slingbox might accidentally be configured to the wrong input. If you have configured your device to use the component inputs, but accidentally have the composite inputs connected, this will cause a disruption in your video signal. Both component and composite inputs use the same Red and White audio inputs for sound. If removing the HDMI cable from your home setup does not resolve the issue, reconfigure the Slingbox M1, and ensure that the correct inputs are selected in the setup that you physically have connected to your Slingbox.
Here is an article that will help you, should you need to reconfigure the device:
While the title of this article might not sound like it applies to your issue, this will walk you through steps on how to reconfigure your M1, and make sure that the inputs are configured correctly.
Hope you find this information helpful!
Sling Media Technical Support