New user - added piece by piece.... : started with Arc Ultra, 2 - 300's, mini sub. ISSUES! Help!

Since it was working try a simple network refresh: power down all Sonos, reboot the router, power up the Sonos.

Once you have the system back folks here can help with the remote. I'm not sure what the net has to do with the remote.

I’ve put a couple of points above in bold. Can you please clarify: do you mean that you can control volume through the app on your phone but not via the tv remote? And secondly, are you saying the Era 300’s and the Sub have disconnected from the Arc Ultra? 
 

If not, can you please clarify these points. 

Just a little tutorial with a question at the end…

Everyone has good reception (access) to the internet as it’s typically provided by your ISP via a cable connected to a modem inside your home. Most ISP’s today provide at least 100Mbps incoming (speed) which is adequate for even Sonos. The only time you would not have good access to the internet is if you are relying on a cell tower service (wireless) to bring the internet to your home which have their own set of issues.

Most home user issues are due to the configuration of their router which is connected to the modem and in turn converts the Internet signal into a wireless broadcast carried over WiFi.

WiFi is subject to interference from internal and external sources which can cause Wi-Fi clients like Sonos to lose connectivity.

Regarding your surrounds and Sub the internet is only required during initial setup. After setup if they are being used as surrounds their functionality is dictated by the Arc Ultra over a hidden proprietary Wi-Fi band. However, Sonos Tech support comment regarding the internet may have been referring to getting them properly setup.

As you live in an apartment do you have a modem and router inside your dwelling or are you sharing the Internet/Wi-Fi via a consolidated community service?