Is the firmware of everything up to date? I would also reboot the LG. too. A strategy that has improved things in other situations is to disconnect all HDMI’s to the TV, power down both units for a few minutes, then power-up the TV and ARC and then reconnect their HDMI cable. The TV and ARC will rediscover each other. Now you can connect other HDMI devices, if any. Make sure that the HDMI cables are fully seated in their sockets.

In situations such as this it is hard to place blame without using some very expensive test equipment. There could be an anomaly in either the LG, ARC, or the HDMI cable. Replacing the wrong unit may not cure the issue.

Do I understand correctly, you recently changed the TV?

It’s always been the LG tv… the issue has been happening since the tv and arc were purchased about a year ago. The setup is just the LG C1 , arc, and a comcast Xfinity top box. I tried the unplug hdmi and power for everything earlier tonight and will see if that works, I also ordered some newer ultra hdmi cords. From what I can tell, the arc just doesn’t get the signal to wake up after things have been shut down overnight. 

I also turned off the quick start setting or whatever it is today… we will see. 

Which power button are you using to turn ON the system? It may help if you use another power button.

Quick start disabled, will just cause your TV to take longer to power on - I would check and disable CEC control on all the devices connected to HDMI ports 1, 3 and 4 (if relevant) and leave the Sonos Arc to get CEC focus.

Also toggle off/on (and leave on) TV Autoplay in ‘Settings/System/tArc Room Name]’ in the Sonos App and see if those few things fix the issue.

None of the above fixed it… I came down this morning and powered everything up and the Sonos is still asleep. No white or green light in front after turning on the tv. I also went into the Sonos app and the system does not show up there… is that normal for when it is in in standby?

 My last thing to try is newer hdmi cords. Other than that I am out of ideas. 
 

It’s certainly is not normal …and the fact the Arc is not showing up in your Sonos App, is ‘inferring’ it’s not the HDMI cable either.

Did you switch off CEC on your ‘other’ connected devices and toggle the ‘TV Autoplay’ feature? 

It would be interesting to see if the issue goes away if you disconnect all other devices connected to HDMI ports 1, 3 and 4 - I would do that just to eliminate the possibility that another device is stealing the CEC (‘Simplink’) focus away from HDMI-2 (ARC/eARC) port.

The drop from the App though is another issue entirely - are you running the setup on ‘SonosNet’ or on your local WiFi? Is the WiFi a mesh-setup, or central router (with or without additional wireless access points) Are the access points wired back to the router?

More info is needed to know exactly why the Arc is not being discovered by the App.

What mobile device are you using as your Sonos controller?

So the arc should still show on the app when it is in standby or sleep mode? It is a mesh orbi wifi and everything is wireless, no Ethernet. I have never had issues with the wifi it’s been very reliable, my app controller is my iPhone. 
 

and yes I have toggled tv auto play. I just plugged in the new hdmi cords and will disconnect the cable box from hdmi 1 when I shut everything down tonight overnight. 
thanks 

There is often issues with Orbi Hubs operating on different channels and not allowing the discovery of SSDP multicast packets between the 5Ghz Band and 2.4Ghz band - the Arc will always connect using the 2.4Ghz band - so my suggestion is to follow the advice in this Sonos Staff initiated thread:

Sonos on WiFi Mesh
 

I would personally suggest switching your system over to SonosNet - that entails wiring a single Sonos device (not a HT surround or sub) to the primary Orbi hub/router. Do not wire any Sonos devices to the Orbi Satellite hubs. Keep the wired Sonos product at least one metre away from your Orbi hub, or other wireless device.

See this helpful support page too:

https://support.sonos.com/en-us/article/switch-sonos-between-a-wireless-and-wired-setup
 

When the above is in place, remove the Orbi WiFi credentials from the Sonos App network settings (Note only do this step if you do not own any Sonos portable products - Roam/Move).

Finally set the SonosNet channel to one not in use by your Orbi Hubs.

Those step should then stop the issue your are having with the Sonos App discovering your devices.

Sort that first and then post back, as we still need to resolve the TV autoplay issue, which I still think will likely be a CEC discovery issue and ‘perhaps’ a different matter to your discovery issue, although wireless interference cannot be ruled out at this stage.

I should add the above post assumes your (ISP Provided?) original modem/router is ‘bridged’ and the Orbi mesh setup is operating in ‘router mode’ and that the Orbi setup itself, is not ‘bridged’ and all hubs acting as AP’s to your ISP router/modem - If the Orbi system is in ’bridged AP’ mode you will need to wire the Sonos product mentioned to the router instead (which should have its own WiFi adapters disabled).

Hope that assists.

There is no ISP equipment just a newer surfboard modem and then orbi is the only router… so no bridge AP I think? Networking not exactly a strong suit for me but will try to look into this all tonight
 

also, wiring the arc directly to the main orbi is not very feasible for my situation. 
thanks

Ah that’s okay I wasn’t sure in which mode you were running the Orbi mesh system - as it’s in router mode, you just wire the Sonos device to the primary Orbi hub/router - if it can’t be done with the Arc, one option is to add the Sonos Boost to the setup and wire that device instead, but remember to do the other things mentioned too, such as keeping it one metre away from the hub and any other wireless devices etc.

ARC being invisible on the controller is separate from any CEC monkey business. There is a network issue. When ARC goes into Standby mode, it should still maintain its network connection -- if the network allows this, and the network should allow this. ORBI should not cast ARC aside. When you reboot ARC it broadcasts a distinctive message that attracts the ORBI’s attention.

I suspect that if you were listening to a music service this connection would go down and the music will stop because it uses the network. Simply playing TV audio does not require any network services or controller activity. TV audio is sent directly over the HDMI connection. The SONOS controller is simply a remote control. Adjusting Volume with a SONOS controller will require network services between the controller and ARC. If you use the TV or COMCAST remote (and have set this up) you can control  ARC’s Volume through the TV’s CEC connection.

If you have not already done this, I strongly suggest that you reserve IP addresses for all regular network clients -- especially the SONOS units.

Have you disabled the ARC’s status (white) lights. If not, ARC will display a dim white status light in the center and, if you have enabled the microphone, a white light off to the right. Unless you are setting up ARC a green status light indicates Mute.

Submit a diagnostic while the system is operating normally and another when ARC is not online. It would also not be wrong to submit a third immediately after ARC comes back online. Keep track of the confirmation numbers and contact SONOS support.

Here we can speculate and share our past experiences, but the diagnostics log details that are only available to SONOS staff. Network issues leave tracks in the diagnostics. Sometimes a staff member stops by here and could comment if you post confirmation numbers here.

Thanks I just got home and powered up the TV… no arc sound (nor signs of “waking up” and the system does not show in the app. I ran a diagnostics 328548354

will try calling… hoping for some confirmation that the boost will solve the issue since that seems to be a simple solution 

The Boost will ‘likely’ only resolve the Arc discovery issue in the Sonos App. The issue of the TV not causing the Arc to autoplay the TV audio, is ‘likely’ to be a separate, (possibly) unrelated issue, but speaking to Sonos Support is always a good next step as the diagnostic information they can see/examine may help to pinpoint the causes. Best to submit the diagnostic report as soon as you encounter the issue and you can contact/speak to the Support Staff via this LINK

Are we 100% certain that an arc that drops the wifi overnight should still play hdmi audio when the tv is turned on?

Yes. The Arc does not require a WiFi signal to play tv audio. Recently my ISP were doing improvements on the network, so I had no internet service. I was still able to listen to the tv audio through the Arc.

Its a different type of connection to the Arc.. one is via HDMI cable, which is an input to the TV and why you should see a screensaver on your TV HDMI-2 port/input, but the audio-out to the Soundbar is over the ARC/eARC link, which is the (enhanced) audio return channel.. it’s why the cable needs heac (HDMI Ethernet and Audio Return Channel) support - the cables are often referred to as HDMI 14+ and most folk here recommend using the cable supplied by Sonos with the product.

The Sonos App and Arc each communicate however over your WiFi network (Orbi). In fact the App uses SSDP (the UPnP simple service discovery protocol) to initially discover the Sonos players and this is done via multicasting via UDP to 239.255.255.250:1900 and, for good measure, broadcasting to 255.255.255.255:1900. 

Thereafter communication is unicast. Allegedly Orbi maybe problematic for this communication if say the Arc is on the 2.4Ghz band (channel A) and the controller device is connected to the 5Ghz band (Channel - just as an example. It can mean the communication packets do not always get through to discover the devices on the LAN. 

So the communication between the Arc and TV is unrelated to the communication between your Arc and mobile controller App. Hence that’s why the Boost (wireless SonosNet connection) is only likely to resolve your Arc discovery issue in your Sonos App. I don’t think it would fix the TV autoplay issue, if you are not getting any sound from your TV - I did hope the toggling off/on of ‘TV Autoplay’ in the Sonos App would resolve that for you, but presumably you have tried that with no success?

I think it’s best to resolve the Arc ‘Discovery’ issue first anyway, as you can then use the Sonos App to at least re-enable the TV audio using the TV icon at the foot of the ‘music services’ tab, that’s if we can’t find a way to get the Arc to autoplay the TV audio.

So that’s why I was suggesting to wire a Sonos device to the primary Orbi Hub to see if you can get the SSDP discovery via multicasting working between your controller and the Arc over a SonosNet link rather than your Orbi WiFi.

Hope that all makes sense to you.