You may see this message from time to time. This is generally due to the web app having exhausted its quota of Google Maps usage. This typically occurs (if at all) around the times of full moon or other prominent events such as eclipses.
It is due to the expense of Google Maps under the new pricing regime. We're planning on making changes to address this in a future update such that such usage limitation are not required.
For further information, please see here.
Thanks for your understanding.