The 401 error stands for "unauthorized". OneDrive sends that error message when the token we send is invalid or out of date. I think you need to reconnect Akeeba Backup to your OneDrive account.
Moreover, I do see something really strange in your backup log file:
DEBUG |161116 11:19:09|Akeeba\Engine\Postproc\Onedrive::Akeeba\Engine\Postproc\Onedrive::processPart - Performing simple upload
INFO |161116 11:19:09|Finished post-processing file <root>/administrator/components/com_akeeba/backup/site-bolsterdorp.be-20161116-101809.jpa
DEBUG |161116 11:19:09|Deleting already processed file <root>/administrator/components/com_akeeba/backup/site-bolsterdorp.be-20161116-101809.jpa
There's no way your 54.6Mb archive file was uploaded in a few milliseconds. However, our code received an HTTP response saying it did! This means that
your host is doing something stupid, namely that they're running a caching proxy server in front of your site. Therefore all outbound connections to OneDrive and the OneDrive OAuth2 facilitator hosted on our site are cached. As a result, neither are the OneDrive tokens updated (hence the 401) nor the upload being executed (hence the backup files being lost). Please contact your host and ask them to disable that crap
immediately. Their server is lying when any script running on it is trying to send or fetch data from an external source.
Nicholas K. Dionysopoulos
Lead Developer and Director
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