When trying to import from Google Drive, the following error is shown:

There was an unknown error with the Google Drive API: {0}.

Any error code ending in -240

The Google server has encountered an unexpected error. Here is what Google has to say on this error:

500: Backend Error
An unexpected error occurred while processing the request.

ShareGate Migrate will automatically retry any call that receives this error response from Google. If this error occurs frequently, contact our technical support team.