Is ARC wired to the network?

Describe your network for us. What model router are you using. Is there a wireless mesh?

I have same issue. It only stays in the app for max one day. Have not found a fix

Just not enough information. A most likely solution is duplicate IP addresses, although it could also be a mesh network issue, or any number of other network issues, which is why @buzz was asking for more data.

I have no, mesh and network is setup as dhcp, so it is not possible to have a duplicated ip adress. I have another sonos product in my setup and never have issue with that one . 

All networks are DHCP, it’s the way they work. 

Given the reticence to provide any significant data, I’ll suggest that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your Sonos system and network.

Having DHCP does not mean you cannot have duplicate IPs.  Reboot your router once and very the next IP lease* reissue could trigger a duplicate IP.  For consumer routers, the vast majority of IP allocation tables are not persistent through a reboot.  Basically the reboot wipes the table out, so the router is handing out IP addresses from a blank allocation table, and could easily hand out one which is already in use on the network.  This can go completely unnoticed, or in the case of Sonos which requires constant communication between devices, it can wreak havoc.  This havoc can be intermittent, or persistent, and can cause everything from stuttering playback, to skipped songs, to missing devices.

*The fact your symptoms are showing up after a day points to a duplicate IP, because the average IP lease is one day, and when the lease is up, a duplicate IP is issued by the router. 

To solve, reboot/power cycle each of these in order:

Modem
Router
Hubs or switches
Wired Sonos components
Wireless Sonos components
Computers, printers
Phones, tablets, all other wireless devices

Note you can prevent duplicate IP addresses by reserving a permanent IP for each Sonos unit in your router setup. See your router manual for details.

I have a similar issue. Era 100 vanishes…..still works though ...

Sonos controllers discover the speakers on the LAN using SSDP multicast discovery (part of the UPnP protocol) - if devices disappear from the App, it’s sometimes because the multicast packets are not transversing the network between controller and the speaker/device - So something is perhaps intermittently interfering/interrupting those packets.

This can occasionally be the mobile controller device itself and software running on that device, such as security software, firewalls, vpn client software etc; or the mobile device might be auto-switching to nearby guest networks or other WiFi access points, especially if those AP’s are operating with different SSID’s, or channels, compared to the main router. Then there might just be general WiFi interference getting in the way (consider trying different non-overlapping ‘fixed’ WiFi channels for the local network, such as channel 1, 6 or 11 for the 2.4Ghz band.

It can also be the case that ‘multicast support’ needs enabling on the router (check your router manual). Other router features like QoS/Optimisation of the network/Airtime Fairness can bring about interruption to the communication too and that causes the controller to not find the speaker/device across the LAN, so see what happens when those things are toggled off.

I would check through your network setup and see if there are any issues in these areas and try to resolve them and all being well your speakers will all stay present and correct in your Sonos App. 

If problems persist however, it maybe best to submit a Sonos system diagnostic report from within the Sonos App when you encounter these issues and note it’s reference and then contact/chat with Sonos Support Staff via this LINK  and see what the Staff can suggest to resolve the matter.

Everything has been working for servel days, after I chanced to a fixed Chanel on my wifi. Thank you