It is likely something to do with the TV. What TV is it and is it running on the manufacturers latest software/firmware update?

Ken

Thanks for coming back.   It's a Samsung QE50Q65.  It's ring the latest firmware. 

Before I connected the sonos,  it always kept the previous sound setting. That said,  with the sonos connected, I cannot use the tv speakers (not that I would want to),it always jumps back to through Arc (is that normal too)?

Can you confirm you have AnyNet+ enabled on the TV and can you also try toggling ‘off/on’ the ‘TV Autoplay’ feature in the Sonos App ‘Settings/System/gArc Room Name]’. If that doesn’t fix it, perhaps then try temporarily removing the ‘other’ devices connected to the other TV HDMI ports and see if that solves it. Let me know how that goes.

That can be related to 6 reasons 

1_TV Auto Play is not activated in the Sonos app under Home Theater in settings for the Arc

2_The volume was muted or turned all the why down on the Arc (which activates mute)

3_There’s a setting in the TV menu somewhere for Auto On when the TV is powered on. Also, turn off the “splash” screen which displays the TV manufacturers name at startup if possible.

4_There’s a peripheral such as a cable box (or HD Fury device) that has a negotiation process for audio

5_The CEC implementation for the TV is longer by manufacturer design

6_As @Ken_Griffiths mentioned there could be an update pending for your model of TV

FYI, I have 3 LG’s (all with an Arc) ranging 2018, 2019 and 2020 and there’s a delay with all. Each however has a different length…the longest being 5 seconds. However, I recently changed Cable providers and that’s when the 5 second delay started with one of the LG’s.

Bottom-line is that in the a absence of an available update or user controlled setting the delay may be SOP.

To all those who have helped,  many thanks. I have managed to stop it allays starting muted.