Check for TV manufacturer for Firmware updates on their website.

Power off both TV and Beam for 30+ seconds and remove/re-seat the HDMI cable from each device. Then power all back on and see if these things resolve the matter.

If no luck with these suggestions, then perhaps post the make/model of the TV back here, to see if others with that TV have the same/similar issue.

It sometimes can help to remove any connected ‘other’ HDMI devices from the TV too and add these back to the TV afterwards, or better still, switch off their HDMI-CEC control in their device settings, if not being used.

Thanks @Ken_Griffiths for your reply. Resolving the issue isn’t really the problem, i can resolve it but it’s around how do i prevent it from occurring.

It’s an infuriating problem where I’m very close to ripping out the sonos system down there. It’s so stupid.

Why should i have to remove my other HDMI devices? 

So that the HDMI ‘handshake’ can be setup again between the TV and Receiver, is the reason that was being suggested. Likewise there is a chance that the CEC protocol is losing focus if the peripherals have CEC enabled.

And there are devices out there that have ‘issues’ with their implementation of CEC,  and they can at times interfere with other devices connecting. Ken’s suggestion helps identify if you have such a device, and his advice to turn off the CEC on that specific device would then allow all the other CEC devices, including the Beam, to work as designed. 

And there are some devices that don’t give you the option to toggle CEC, in which case there are small and inexpensive adapters that block those particular pins on the HDMI connection. 

OK thanks guys. So yet again, I have gone downstairs and my ‘lounge’ sonos is connected to the radio, and not the TV- no-one has selected anything other than the TV today so there is no reason for this.

I switch the sonos to TV, no sound plays

I turn the TV off and on, sound kicks in.

Are you advising that I unplug all HDMI devices, other than the arc HDMI connection and see if the problem persists?

The suggestion is to power off (not standby) your TV and Beam completely. Remove the ‘other’ HDMI connected devices from your TV (just as a temporary measure). Power on the TV and Beam and use for a while, just to see if the problem persists, or if the Beam then works correctly and that the Autoplay feature works when the TV is powered on. Give that a try for a short while and  let us know how that goes.

By the way what is the TV make/model and firmware version …and what ‘other’ devices do you have connected to the TV HDMI ports?

Thanks @Ken_Griffiths I’ll try this later on and revert.

It’s a panasonic TV, never had any problems like this before.

I actually think the problems started to occur when I removed my virgin tivo box and added a HUMAX FVP-5000T 500 GB in it’s place- do you think that could be causing problems?

Yes maybe, I currently use the VirginMedia TiVo V6 box too - I don’t know much about the Humax box,  but setting up the handshake again later may resolve this but let’s see what happens when the ‘other’ HDMI devices are left uncabled. If the issue stops, there are several things you can go onto try afterwards.