Christopher
After some remote help from China that probably was not so helpful, I have been able to install the latest firmware and the NAS seems to be working properly now. Had to start from scratch again so everything on NAS deleted. Good I don’t trust any NAS for backup solutions 
I’ve made a new case as restoring backup is definitive not working on either the Qnap, nor the SonicTransporter with a new M2 SSD, so I guess this issue should be handled by Roon support.