We experienced intermittent issues with Google Calendar's API starting yesterday (March 11th, 2021). This may affect viewing calendar busy times as well as guest booking.
This is an issue on Google's end. We're keeping an eye on it: https://issuetracker.google.com/issues/182497593
Note: this issue may have already be resolved, as we haven't seen any new errors in our logs from 11pm PST onwards.