Can't add a certain VM to a existing Replica-Job

[DK2000]

Running latest Veeam v6 and started from scratch but I just can't add a certain VM into one of the existing replica jobs. I add the VM, the backupsize is increased (in the replica wizard) and with the final step it still is listed but once I click "Finished" it just isn't added to the job (still 6 instead of 7 "objects in job"). When I reenter the job properties, the VM is not in the list, BUT when I enter the "advanced guest processing" options it IS listed?!?

Also:
- Creating a brand new job with that vm works just fine
- adding any other VM with the old replica-job works just fine

Is there anywhere a log-file which could tell me why the VM is not added properly to the replica-job?

Sure I just could re-create the old job or add new one and but:
- I don't want to loose the replicas so far (or would veeam "import" that old replicas ?)
- I don't have all login-credentials and the admin ain't around till next year...

[Gostev]

Log files can be found under Help > Support information.