I cant control my volume when I play music over multiple deivises/groups

First, a clarification. Your combination of Arc, Sub and surrounds is a “room” in Sonos terminology. They should be identified as a single entity in the app: have you called them Living Room? Then you suggest you have stereo-paired two Era 300’s, which you have set as a differently-named room. 
 

Is that how you have the system set up? 
 

Sonos lets you “group” two or more “rooms”. If you have your system set up as I’ve suggested, can you please re-describe your issue? You cannot “play over two groups” as you say in your question. 

Yes, indeed I have one room with the arc/sub/surrounds.   One room for the Era 300.  When i go to play a song using both rooms, as soon as i touch volume slider, music stops.  Can't seem to control volume over two room?  (i have 4 Sonos one sl’s in two different rooms and i can move volume up and down with out any issues. 

It’s an odd issue! Have you tried powering off all speakers and router, and then restarting? And perhaps deleting and reinstalling the app? Are all devices up-to-date?

I just added the 300’s today. The rest of system has been in operation for 3 weeks with no issues.  I will try what you mention and see how it goes.

thank you