Managed Backup is not working.

Managed backup is smaller than the earlier backup. The earlier one is 6gb while current one is 2.3Xgb. Though we have not made any changes to the site. The log says

[snapshot] [2018-01-12 01:22:12] [Warning] There was an error processing the files
[Cron] [2018-01-12 01:22:15] [Error] Error processing, automatic backup: unknown: unknown

The memory limit is set to 1024m and max_execution_time is set to 300. On my site it is showing that the Managed Backup size in the hub is 107mb whereas the site is about 6gb and this 107mb backup is also not showing in the Admin Managed backups list. It is only showing in the Hub.