My guess would be a permissions issue? I don’t know what user the QNAP app runs the container as, but if that user doesn’t have read access to those files, it could show as file not found.
Side note, your identity folder only needs the identity.cert and identity.key files. The numbered files are backups made during the key signing process, and the ca.* files are used as part of the certificate creation process. Best practice would be to backup the files other than identity.cert and identity.key to a separate, secure, and ideally offline location.