Duplicati is working extremly slow


i run Duplicati - to backup my files on a QNAP 4bay NAS.
2 Bays have the HHDs for the Data, the other 2 Bays are there for the Backup.
I created a backup plan and started it, but it is working really slow.
Encryption is not on, but i still see only a transferrate of up to 10 KB/s.
Since it is a NAS internal backup it should run much faster i think.
What can i do to solve this problem?

Is this the first backup? These can be quite slow due to lots of database overhead - especially on limited hardware such as many NAS devices have.