No, I have all the QNAP media software disabled. I also don’t use the preconfigured media folder/share for my local Roon audio library. But you may need to install the ffmpeg codec as the one from QNAP is crippled.
Where does the Core on the QNAP point to? Is he configured to use the local path to the music files or is he configured to use its own network share (I would try to avoid that)? Did you load a backup from the iMac Core that still points somewhere else and causes the trouble?