I'm not certain if the issues above are the same as my problem. I can use UpdraftPlus to back up to Dropbox. Yet Google Drive is problematic. After UpdraftPlus sends between 70% to 90% of the chunks to Google Drive, I get a Google Drive Upload Error. The 401 error states the problem as 'Invalid Credentials.' Then, UpdraftPlus starts sending chunks from the beginning again. This doesn't always happen in the same spot in the backup. Sometimes it happens around the 70% point, sometimes it makes it to the 90% range before it errors out. Also, I was able to get it to back up successfully after several retries over the course of three days. Here is one of the sections with the error:
5908.777 (9) Googledrive chunked upload: 72.6 % uploaded (608436224)
5909.268 (9) ERROR: Google Drive upload error (Google_Service_Exception): Error calling PUT https://www.googleapis.com/upload/drive/v2/files?uploadType=resumable&upload_id=AEnB2UCvBDY3A: (401) Invalid Credentials (line: 79, file: /home/content/p3nexnas05_data03/50/2104150/html/wp-content/plugins/updraftplus/includes/Google/Http/REST.php)
5910.196 (9) Googledrive chunked upload: 0.1 % uploaded (524288)
5910.744 (9) Googledrive chunked upload: 0.1 % uploaded (1048576)