Are both CONNECTs part of the same system? I.e when you open the controller, do you see ‘both’? If not, you’ll need to factory reset one of them, and add it as a ‘new device’ to the other system, using the controller. 

You state “both are in the same group”. Since “group” is a Sonos term, I am confused about what you mean by this. A Sonos system consists of “rooms”(either stand alone speakers or fixed stereo or surround set ups) that can be “grouped”, see https://support.sonos.com/en/article/group-and-ungroup-rooms. On top of that multiple rooms can also form “zones”.

In this sense you saying “both are in the same group” confuses me.

I found the problem.  Thanks for all the suggestions.  

The line level output was TOO LOW for the connect system, so even though it showed the line in as active there was not enough impendence to work.  All is good now!