I believe each time any manufacturer updates an app or OS, there are going to be issues. Most people don't like change, as most of us are creatures of habit. I doubt Sonos will revert to the old app. But they will get the issues sorted out.. in time. This is what happened when the old S2 app was introduced: people complained.

I agree that the new app has a learning curve for all, but I don't hate it. Its inline with many other apps on the market. You just need o spend some time exploring it. I would like to be able to customize it and have my most used functions on the home screen or a second page.

If you are also unable to find your system from the PC app, you may have network issues. Most people believe their network is solid, but there could be some minor config issues.

If you do not already have a speaker hardwired to your network, connect one to see if that helps. Only connect a main speaker like a soundbar or standalone like a Five or One. NOT a Sub or surrounds.

If you are able to do an IP reservation on your router and give your Sonos speakers static IP address that will also help.

Nothing to do with not liking change.  The new App simply doesn't work reliably.  Response time to commands can be many seconds, assuming it does even eventually respond correctly.  And don't try and tell me I have network issues. I don't. My Internet is fast. e.g. Response to cloud based Alexa voice commands and questions is virtually instantaneous.  So why the problem with the new Sonos cloud App, unless their servers are not up to the task?

Jon,

Your internet connection may be fast, but that doesn’t necessarily translate to the connection between your router and the speakers. While it might be the app, it could also be a duplicate IP address, or some other local network issue between your speakers and your router. And music isn’t a single point transaction, like an Alexa request/answer. Duplicate IP address issues come and go, depending on which device is ‘connected’ at the moment. Which can change.
 

Be open to other possibilities, don’t assume one thing, when there are multiple potentials. 

Once you’ve decided the problem must be e...] or cannot be e...], you are likely to be blindsided. Further, mother nature is not fair. There could be multiple issues.