I’m having the same issue since the update to allow Google Home to access SmartThings routines.
Previously, I could explicitly exclude devices (Rachio sprinklers, etc.) from Google Home voice control.
I also had the ability to refresh SmartThings from Google Home to add/remove devices.
Now, if I add a new device to SmartThings, I have to disconnect SmartThings from Google Home entirely, then reconnect it. Unfortunately, this loses all my room assignments, which takes forever to restore manually.
I had to disconnect Rachio, Sonos, and Harmony completely from SmartThings before I reconnected it to Google Home, or Home voice commands like “turn everything on” would turn on all my sprinklers, speakers, etc. even when all I wanted was my lights, switches, and outlets.