I have something similar. Today I received several Emails like this:
The refresh token for one of the OAuth services Google on your site https://[moodle] has expired. This will limit the functionality of any plugins that use this service. To fix this issue, visit the OAuth 2 Services configuration page and click on the "Connect system account" icon in the table row for this service. Be sure to login using the same service account for the OAuth system each time.
Everything seems to be fine in Moodle however. There's a green mark behind the 'system account' in the Oauth screen.
Seems like I can ignore these Emails....