The controller is having trouble discovering the player(s). Describe your network for us. What’s wired and what’s wireless? Which wireless bands/channels? 

For iOS it might help to disable WiFi Assist and Private/Random MAC addresses.

Hi, everything on the network is wireless, there are no wired devices into the router which is a Talktalk router: 2.4ghz channel 1, WPA2 security.

I’ve already disabled WiFi Assist and Private/Random MAC addresses having seen the articles on this site.

Does the phone have any kind of VPN installed on it? 

Have you scanned to see if channel 1 is the best option, taking into account neighbours’ signals? Or perhaps simply tried a different channel, such as 6 or 11? 

Hi no vpn on phone but I can experiment with different Wi-Fi channels, I’ll give it a try and get back to you…

I tried with different channels and it seemed to fix it but a while later it started happening again ie unable to find your system then it corrects itself and connects. I’m not sure if other people using iOS see this periodic disconnect connect problem but it doesn’t seem right…(thanks for all the help btw)

Does the behaviour change depending on which WiFi band -- 2.4GHz or 5GHz -- your phone connects to?

Rebooted everything iPhone and sonoszp were both on 2.4ghz and it seemed stable…went away 10/15 mins and noticed Sonos app couldn’t connect…sonoszp was on 2.4ghz and iPhone had moved onto 5ghz now seems to be frequently connect/disconnecting

It sounds like the router could be a possible culprit then. Some home routers aren’t great at forwarding the broadcast discovery packets between WiFi bands. The Sonos app relies on this to connect with the players. 

A quick google for “sonos talktalk routers” suggests others have encountered similar issues.

So you reckon because sonoszp is on 2.4 and iPhone on 5 that causes the disconnect because they are on different frequencies but it shouldn’t be an issue because the router should handle it? 
I don’t suppose (if this is the issue) there is a way of rooting two devices to the same frequency so they are always together?

The Arc always connects to 2.4GHz.

If you’re able to configure the router to use two different SSIDs (WiFi network names) then you can obviously force your phone to use the 2.4GHz one. (Turn off the iPhone’s Auto-Join for the 5GHz SSID.)

Out of the box many home routers now “helpfully” have a common SSID across both 2.4GHz and 5GHz, and use a “smart connect” (or some such) approach to decide which band to connect the phone to. If the router is deficient in other respects -- e.g. not forwarding traffic transparently between bands -- this is “unhelpful” for a system like Sonos which relies so heavily on intra-LAN comms. 

Ok I’ll look into this and experiment. 
I think you’ve nailed the problem thanks for your help.

Excellent advice from others. Here’s another possible issue with your iPhone which is storage.

• Go to Settings > General > iPhone Storage

If the iPhone storage is close to being maxed out the Sonos App can’t load properly. One way to free up storage without deleting anything is to Optimize your photos via iCloud (assuming you’ve setup iCloud storage beyond the free 5GB).

• To Optimize photos > Go to Settings > Click on your name > iCloud > Photos > Optimize iPhone Storage

The process is not instantaneous and will take some time to upload to iCloud. If you’ve already set photo’s to optimize then you’ll have t consider deleting apps and their data and/or removing old messages. 

As I said earlier the above is only relevant if the issue happens to be related to your iPhone storage.

Hi thx for your answer: I have about 99Gb free on my iPhone so I think it is okay for storage.

Good to know it’s not a storage issue