For all Google Docs, I\'m not able to download the thumbnail image from the ThumbnailLink property returned with a file response.
I always receive a \'403 - Forbidde
As far as I can tell, this is a bug with the Google Drive API. As you've stated, this problem appears only for Google Docs format documents, not uploaded files.
I am getting the exact same type of error message as described in my post.
Also as you mentioned I believe this had been working a short time ago.
The problem we're getting now didn't happen when we were using the deprecated Document List API. We're switching to the Google Drive API with OAuth2 as part of updating our marketplace application in order to be listed on the V2 Marketplace.
It has been extremely frustrating to not have any feedback from Google developers who are probably the only ones that can reply about whether this is a problem with the Drive API.