I'm guessing you actually have either the Google Nest Hello Doorbell, the Google Nest Doorbell (Battery), or the 2nd Gen Google Nest Doorbell, and not a Ring Doorbell, or you would not be posting here in the Google Nest Community forum.
Motion alerts depend on how you've configured your activity zones. You can restrict alerts to events that happen in certain zones in front of your camera. If you don't, the camera can pick up motion from anywhere in the camera's view, like out in the street from passing cars or pedestrians. The settings vary by the specific doorbell. We have Nest Hellos, so I can only speak to those. On our front door Nest Hello Doorbell, I have alerts turned off for the zones that cover the sidewalk and the street, or we'd get alerts all the time. But we can still find the events in the doorbell's history.
Sometimes rain or snow can also trigger motion events.
If none of this explains what's going on with your camera, maybe something wrong is going in with your doorbell. How old is it?
I’m sorry for the trouble here. Let’s sort this out — a few questions: were there any changes to your Wi-Fi network? What’s the make and model of your phone? Do you have a Nest Aware subscription? Also, have you created Activity Zones for the camera in question? Are Alerts enabled for the Activity Zones?
There are a few things that can trigger unwanted alerts or false positives, here are common triggers to name a few:
I appreciate the help, MplsCustomer.