I recently purchased a Nest camera with floodlights. Like everyone else, I too was disappointed that I could not add this device to my nest account. However, I have noticed that ever since the new camera with floodlight was installed, the audio portion continually lags while viewing through the google home app. You can hear the sound for a moment, then nothing. This cycle continually repeats itself to the point it is maddening. Meanwhile the cameras are all displaying a picture. I can open the Nest app and the audio/visual display works well, but I cannot add the camera to this app, rendering it relatively useless. I've also noticed that the same lagging begins to effect other apps on my phone, causing me to restart the device after I have viewed any video in the home app. It seems like closing the app does not sever the connection.
I'm just another Google Nest customer, but the audio lag you're reporting--especially affecting your other apps--sounds quite strange. Our Google Nest Camera (Battery)--which is quite similar--does not exhibit those symptoms.
The newer cameras do NOT appear in the Google Nest app. However, Google Nest has a preview version of https://home.google.com that went live a week ago and includes all of our cameras.
And they've announced an upcoming upgrade to the Google Home app. I don't know whether that will add Nest app functionality to the Google Home app for our older cameras, but I really hope so. We're tired of having to use 2 apps for our cameras.
Sometimes you can resolve Google Home app glitches by deleting and reinstalling the Google Home app. We had to do that on one of our iPhones when we stopped getting notifications on just one phone. You don't lose any setting; after reinstalling, you just log back in.