Cannot transfer archive to Amazon AWS when several machines were offline

Hi,

i have a really strange problem:

Sometimes the transfer of the archive to Amazon AWS fails. In the details i get the error message:


Exception chain:

  • Der Wert darf nicht NULL sein. Parameter name: source
  • Mindestens ein Fehler ist aufgetreten.

and for every machine i get a mail 

Quest Core auf BACKUP hat das Error-Ereignis "Core backup has failed" gemeldet:

Datum/Uhrzeit: 05/03/2019 01:00:07 +02:00

A scheduled backup of the protected machine 'Computer xxx xxxxx' has failed.

An unexpected error occurred

An argument was unexpectedly null in code located in or called by 'EnumerableExtensions.ForEach'
---

Informationen zu diesem Ereignis: A backup of the Core has failed

https://backup:8006/apprecovery/admin/

I found out that the problem only occurs when a machine was offline for >1 day. Then this error occurs for every machine. When i deselect the offline-machine then the transfer to AWS works again.

In my case oneworkmate was out of office for a few days. After the machine was offline for a day the transfer failed. I removed his machine from the archive and forced a transfer and everything worked again.

The same problem occored with the machine of another workmate. 

The Core- and Agent-versions are 6.2.1.0.0