Add a Google Home into my google mini's network

I have 3 Google mini (working perfectly) and created several rules. No problems with them.

I added today a Google Home (better sound quality for music) into my Google home settings: NO problems (same Google user, same network). Ran the usual tasks: integrate into my network (static IP), added to my user account, listened to music (built-in and through Airfoil/BubbleUPnp (btw thanks to the guy who posted that, very nice app to swap from speakers to speakers (GM, GH, Sonos, Vizio sound bars). So, everything is OK

Added to HE: rediscovered the Chromecast integration (OK), added the new "device GuestRoom". (OK) Then I wanted to update some apps related to my group of Google devices...

To keep things simple (I'm a beginner here), my apps are: say time at 9pm, say time when a virtual button is pushed, mute them all at 11pm, unmute them all at 10am, etc.
Of course I wanted to add the new GuestRoom Google device on those existing apps.

On some, I can. On some, I can't (errors). See summarized pic.
I rebooted HE: same results
I shut down HE: same results

This is not difficult to recreate those simple tasks but I wanted to submit the problem to you, in case of.

Mike

Why are you setting the volume to 1 after you've muted them?

I'm on test for now. Because you can't set the level at 0 (support will try to discover the flaw), so I put both (not needed obviously, will remove one).

But, for any reason, is it better to play with the volume only (from 0/1 to 100) or keep the volume level and mute the unit ?
I don't find any advantage/disadvantage yet.
Any idea/suggestion ?