We need more information to assist you.

Are you referring to a Sonos Arc + Sub + One SLs as surrounds? Do you get any audio from the Arc from any source from the TV? Do you hear audio when streaming music from the Sonos app? What model TV do you own? Is the Arc connected via HDMI ARC or optical? What specific model is your cable box?

I have Fios, a Samsung Series 8 TV, and a playbar.

am routinely finding that I get no sound when turning on TV. I have to reboot Fios box and the sound starts working. Cannot figure out why.

Do you have TV Autoplay enabled under the Playbar’s settings in the Sonos app?