We recently reset our speakers (hubs, hub max, audio and minis) after a wifi change. Now, when we try to play on a speaker group only 1 device plays (when 4 should). We have deleted groups, made new ones, changed devices included in group and haven't had any change.
I have a similar issue. I have a Nest hub and Nest audio and I tried creating a group but when I play music only one speaker plays. It works sometimes but many times it does not. I tried doing a factory reset on both. It worked for a bit then same issue. I tried uninstalling/installing Google Home app. No effect.
This is not the experience we want you to have, let me help you. A few questions: which Nest speakers are we working with? When did your issue begin? Were there any recent changes made? What is the distance between your Nest and Wi-Fi devices?
It would help a lot if you could do a sequential reboot first:
Let me know how it goes.