This statement:
is inconsistent with this:
I'm going to assume you've used both with the same device (really device ID, as you might see in the URL of your browser when viewing the device detail page) because that makes sense given what you are seeing.
I asked because Generic Matter Thermostat changes some device data that will permanently alter the device to use a "new" parsing method, which is why your temperature data (or really any attributes/events, but perhaps that's all you get reported) is erroring out rather than populating the value. A future platform update will ensure this does not happen when changing between these two largely incompatible types of drivers, but for now, the easiest thing to do might be to remove and re-add the device, making sure you do only use the Google driver (or "Device" as it might pair with if nothing matches -- hopefully the generic one doesn't first!).
If that doesn't help, there are some tricks you can do to remove this data if you don't want to wait, but it will need a custom driver. I could write one quick or probably point you to a community offering that does -- actually, I know this one does: [RELEASE] Matter Advanced Bridge (limited device support), and you might actually want to take a look to see if it handles your device features better (can't hurt to try before you remove and re-add the device if you're going to do it anyway 
).
Hopefully one of those things helps!