I have the same trouble - all of a sudden.  I have been using the era 300 with no issue for months and I went to use it this evening and no dice - I have factory defaulted it 4 times tonight - I am so frustrated.

I have the same problem. 

I’ll be calling support as soon as they open tomorrow. I’ve tried many times again today with no improvement. I’ve restarted my network, I’ve tried from multiple mobile devices. I can see the Era 300 connect to my network.
I’m frustrated that this coincides with the launch of the new app. It feels like it must be related, but I cannot qualify that feeling. 

Same and glad to know I’m not the only one. If you do get a solution would you mind responding here please @mooneb 

I will post what I learn, for sure - I have a 75 minute estimated wait time.

Thanks. I’ve rebooted router and phone, factory reset brand new 300 speaker and made sure I’m on the same wifi with VPN switched off. No joy. Two other speakers connected fine a few months ago.

Well, I waited two hours to be told there nothing to do but wait for an update to the app. They will not put version 16.1 back on the App Store. My case is escalated, so we will see where that heads. 
 

I know it’s the app. The amount of threads that are s8milar is staggering. The wait time is telling. They could not get an engineer on the line with me and I felt shuffled away. 
 

While I waited, I did verify that I can use Spotify connect and AirPlay so I know the speaker is not the issue. It is the app. I hate to say it but they really screwed this release up. I’ve begun looking into how to downgrade the app, I have found the installer, I just need to get the iTunes approach working for me. Once I figure that out, I’ll report back if going backwards helps. 
 

I know in my bones it’s the app… I make my living supporting systems. That said, I’m appalled at the approach by Sonos support for this, so far. I’m trying to have faith they will come correct. 

The app was updated a few hours ago - I have found success.  My app is updating the device now after adding it to the system.

Initially it was not discovered, but I then restarted my phone and defaulted it one more time for good measure and that seemed to do the trick for me.

Best of luck to you guys as well

perhaps I spoke too soon - I am connected via my Mac, but my phone still fails to add the speaker.

And now the tables have turned - I got it connected to the phone but lost it on the mac - at least I got to run TruePlay

They have really messed this update up.

I tried again, nothing different and everything is connected.  Hope you guys find similar success

Yes it does work now. I had to delete the app and download it again. That and a factory reset on the 300 got it linked up. Thanks for looking into it

Cheers @mooneb.

Got it up and running. 

How? I still get either an error while adding the speaker or trying to update it (error 1002). Tried billion times this entire week, no luck..

Error 1002 looks like a different issue where the device is failing to complete its update.
 

I’d factory default it. Make sure you’re on the latest version of the app (remove it, reboot your device and redownload it) and start fresh. 

I’m still get the 1002 error trying to set up my five. Still no luck..

I had an issue with my network last night.  It is all back to normal now and I am back to stuck with the Sonos Era 300 - I am so frustrated…  Will keep trying, but it looks like the stability is not where I thought it was.

I can (again) see the thing on my network.  I can (again) restart or default it and have it connect to the network but not the app.  I follow the process and it is a seemingly endless loop.  Again. 

Airplay works - so frustrated.  I really wish they’d just let us download the old app…