Today I have noticed that one of my devices (Neo CoolCam Dual Light Switch) is missing one of the switches out of the two (odd as it is a dual switch) within Google Home. So I went to the Smartthings App and checked it was still joined and working and it was but not showing in the Google Home App. So I then checked the SmartApp tab to see if Google was connect there but is was missing. So I went back to the Google Home App and ‘reconnected’ Smartthings to Google but still the same, not showing in Smartthings App under SmartApps and not re-appearing in my Google Home App.
Look under the hamburger menu (top left) thrn the gear menu (settings menu next to your user icon), Finally linked services. This is where Amazon, Google and a bunch of other services link in now.