Try turning off wifi assist on the iphone 

It was already off. Still nothing. 

I should of added to the OG post that I am using SonosNet, but recently have wired some of my 4 Sonos Play 1 speakers. Still in the process of wiring the the rest of my Sonos. But all is on Boost SonosNet. Not router wifi.

Did you try fully closing the Sonos App (slide off screen) and then simply rebooting your iPhone and perhaps ensure any security software is switched off temporarily (if installed)?

There is a new feature in iOS 14.2 (and higher) called ‘Private Address’ in the WiFi connection property settings, so you could try switching that off too, as it is (supposedly) causing an issue with some routers, but I would have thought that might have applied to your iPad Pro too, but it might be worth toggling off that feature, just to see if it resolves the issue.

I closed the Sonos app and everything else and rebooted iPhone. Also turned the Private Address off with no results. Still no control with iPhone, but iPad is fine. 

Not so fast. When I switched the Private Address back to “on” I rechecked iPhone and looks like everything is back to normal. So far. Weird.

There have been some issues reported online about the new ‘Private Address’ feature being problematic with some routers - so it could be that new feature may have ‘glitched’. I would just see how it goes, now that you appear to have things working. I suspect though it’s an Apple issue, rather than a Sonos one.

Yes I thought it was an Apple or Apple related issue too. Especially when my iPad and computer were fine. I would never of found the problem without your help. Deeply appreciated and thank you. 

Apologies for coming back to this again, but I guess the fix was a temporary fix. I’m back to nothing on my Sonos App again. I tried the “Private Address” switch again. But nothing happened this time. So anymore guesses? 

What wireless network system are you using, is it a mesh system or central router? - do you have any other WiFi access points in addition to the primary router?

Sorry for the delay in my response. So I am running wifi off my month new Boost (SonosNet) which I recently connected to my TP Link router which is connected to the modem. I had been running Wifi off the TP Link all this time. And we also have a Netgear Wifi extender downstairs.  I currently have 6 networks to choose from for my Wifi connection. 2 of which I don’t use much of anymore since we got the TP Link router. So of the 6 networks I really have 4 to choose from. Not sure why Theres 2 networks o can use off the TP Link router and the other 2 are also the same but for the Netgear Wifi extender. I have 2 boys in the house that are online gamers. But I believe both are using Ethernet cables. One recently bought a 5 port switch and cables for his room. The Boost is in the same room as the TP Link router and the modem, which is not occupied at this time. I guess you could call it our central hub for our network. So like I said I just purchased the Boost a month ago. All my Sonos, except for the Move were running off SonosNet. Last week I decided to make Cat5e/6 Ethernet cables for all my Sonos. I currently have 2 of the 3 rooms connected wired now. With the TV room (2 SonosOne/Sub/PlayBase/Port) remaining to be connected. So back to my sons room who has the 5 port switch. He had 2 ports not being used. So I made 2 Cat6 cables and connected to his switch (which he uses for his gaming) and ran them from upstairs bedroom to downstairs to my garage where I have 2 Sonos Play 1 paired. The other room that is wired is my bedroom (2 Sonos Play 1 paired) which comes off a 5 port netgear switch from the modem. I was wondering if I should connect this to my TP Link router instead? It was an existing line for cable box. On my Apps About My System all Sonos are WM: 0 except for Move which is WM: 1. 
Fast forward to this morning when I woke up and received your message. I decided to go into my phone and change to another one of my networks for Wifi. I changed to the same network name but with the extender on it. Does that make sense? Example, from cbe3_2gext to cbe 3_5gext. And what do you know? It’s working, again. Yes the Sonos App on my iPhone 11 is working, for now. Everything looks to be normal on the app. So I am using the _5gext as my Wifi on iPhone and using the _2gext on my iPad. 
I have another issue regarding my sons gaming and cat6 cables. Does my 2 Cat6 cables connected to sons switch have anything to do with slowing his computer down while playing games online? He says ever since I connected  the 2 Sonos cables to his switch his gaming is slow. Do I need to get another switch for my Sonos?
 

Of course it’s not working again. I go out for my hour + morning walk and come back to nothing showing on my Sonos App. Both iPhone and iPad know not working. I switched back to my previous network, and nothing. I give up.

Update #?:

I went to our room with modem and router to check and make sure those were working and fine. I reset both modem and TP Link router several times, messed with the Ethernet cable, unplugged the ethernet cable from router to Boost. Still nothing. I then proceeded to try the Sonos App troubleshooting for wifi. It asked for me steps with the Move. It ask to make sure it was powered on (white lite) and connect it to the router. Know I know there is no Ethernet port for the Move. So why would it ask me to connect it to my router when you can’t? So anyways my Boost is in the same room with the modem and router. So I disconnected and reconnected my Boost to the TP link router and continued the setup for Wifi on my Sonos app. And guess what? It worked. All of my Sonos showed up on my App, except for Move. It’s not there anymore. And then I see my Bedroom Sonos has an issue. I clicked on Bedroom to fix the issue and it shows me an update for iOS 14.2 that needs attention. At the moment I am updating my iOS to 14.3 on my iPhone. According to Sonos Support Home Page it shows a Partial Outage. I’m hoping this iOS upadate will resolve all this pain and suffering with my Sonos App? 

Dcgman#1,

I suspect your mobile iDevice is losing sight of the Sonos devices, as it switches between the TP-Link router and it’s different WiFi networks and your Netgear extender and it’s different networks.

If any networks, like guest networks, are not being used, I would switch those off, and if possible maybe consider having just one 2.4ghz network and one (linked non-isolated) 5ghz network - so you could have on the TP Router, for example... LocalNetwork-2G and LocalNetwork-5G. Just use whatever names you wish for these SSID’s, but name them differently for each band.

Set the 2.4ghz band up with a channel-width of 20MHz on ‘fixed’ non-overlapping WiFi Channels 1, 6 or 11… perhaps try Channel 11 to begin with. Set the 5ghz band channel-width to 40MHz and perhaps begin with ‘fixed’ channel 36.

Once those are in place set the Netgear extender to use the exact same subnet and credentials (SSID/Password). Also use the same channels (11 and 36) for the 2.4ghz band and 5ghz band and the same channel-widths as those suggested above. Also switch off any guest networks on this extender device.

Doing the above, will provide you with WiFi coverage to the premises with a single 2.4ghz signal and a linked 5ghz signal on one subnet as you move about the home with your mobile, and portable devices.

Next you need to leave the Boost wired direct to your main TP-Link router, which is linked to your ISP modem. Set it’s SonosNet channel so it’s at least 5 channels away from the 2.4ghz WiFi band - so set it to channel 1 (recommended) or channel 6. Also keep the Boost at least 3 feet away from the TP-Link router and other wireless devices.

I would also suggest putting both your Sonos Move and ‘other’ (non-Sonos) WiFi connected network devices, where practicable, onto the 5ghz band.

Then all being well, your Sonos products should work fine. I suspect at the moment all your wireless networks are perhaps causing interference and my thoughts are the above suggestions will go a long way to resolving the issues.

Thank you one more time Ken. Before I read your message let me explain what I just did. After I updated my iOS to 14.3 on both iPhone and iPad everything appeared back on both iPhone/iPad except for the Move and paired Sonos Play1 in Bedroom. I tried to get my bedroom Sonos Play1 back but failed. When I reboot (unplug power) I would get a solid yellow/amber light on both speakers. Looking at the troubleshooting led lights there is no yellow light. Only orange. So I went online for help. The Sonos guy assisted me through steps to get my Sonos1 back in my app. Which was successful. The yellow led went to flashing orange and then to solid white. Check my app and the Bedroom showed up. Playing music fine. Moved on the the “Move”. Same thing he helped me get my Move back on my app. So everything is showing up and playing in the house. It was probably the update on iOS that was giving me all the issues the past several days? Fingers crossed I won’t have anymore issues with the S2. One other note, I had both the older S1 app and S2 app on both iPhone and iPad, which I just deleted. So I only have the newer S2 app. I will make note of your last message in case I have issues again. I shouldn’t though. But you never know. Thanks again for being patient with me and all my questions. You have been a huge help the last couple of days. 

Thank you so much for this information.  Was just about to contact Sonos as the iPhone app just could not connect to my Arc, Sub and 2 one SL’s, no matter which route i took through the apps connection wizard it simply would not work.  Then i noticed my iPad seemed to connect ok.  It turns out to be that private address option on the iPhone, turning it off works.

Apple really want you to turn this option on though, we now get security alerts highlighting it being off.  Bizarre thing is it is turned on on the iPad that has always worked.  Sonos should probably try and make their app work with the option turned on otherwise they are going to get a lot of support calls as it defaults to on.  My router is BT smart hub 2