Update on this - Backups worked Tuesday Wednesday and Thursday, failed again Friday Saturday Sunday and today.
Today in particular had a different error message - The underlying connection was closed: A connection that was expected to be kept alive was closed by the server. > Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. > An existing connection was forcibly closed by the remote host
I have sent Advanced log. Seems like someone else is having similar problem recently for OD4B as well Backup to OneDrive for Business Error