The Google Home app has bad refresh rate/hysteresis for entity status.
I have HA itself exposed through a reverse proxy and it’s snappy as can be over WAN. Google Home app/voice assistant is also very quick to send cmd such as on/off for switch and have never had an issue but when I use the home app and click to toggle a smart switch for example, the Home app UI will exhibit following behavior: off → (tap card) → on → off → (5-10 sec later) on
EDIT:
I’ve gotten it back to the mostly working state I had it at, have to add device to a room from the Linked to you section at bottom of app. Still bounces from on → off → (1sec) → on in the UI but it does right itself at least. Also looks like it’s a bug Google is unwilling to consider fixing: Google Issue Tracker
I’d still like to fix it so it doesn’t bounce but I can live with it