What do you mean by randomly turning off? Please give an exact example of what you are experiencing so we can assist you.

My Sonos Beam is playing music the randomly shuts off and flashes a white light. 

Does the Beam do this only when streaming music or does it also happen when playing TV audio? What model router are you using? Is the power cable fully inserted into the Beam? Is the Beam plugged into a power strip? Have you tried unplugging the Beam from power for a couple of minutes and rebooting your router?