Since then Roon is unable to find core.
I have the core installed on a SSD drive attached to the NAS. Since the upgrade I have been unable to access this SSD drive as QNAP say the SSD drive or the core has no digital signature.
Does this mean Roon has to provide a new signature? Or is it a SSD issue?
There might be a Roon logo shown but what is it actually?
Do you probably have issues with viruses on your NAS? Something is obviously off with your NAS and you may have to reinstall the current RoonServer app from the app store. You may also have a look at the projects home page and/or the #roon:qnap-synology forum section that deals with the community support for the NAS packages to get an overview.