Hi Peter.
I refreshed the Roon folder structure (RAATServer) as instructed as well as cleanup but finally narrowed down to AAC files. You did make an initial comment regarding this.
The QNAP (TVS-472XT) is reporting no disk errors but happy to provide smart reports later.
I find when attempting to play any AAC file, the Roon core locks up and I have to restart the Roon server service to allow me to stream anything else.
I found this recent article and looks like QNAP firmware compatibility is to blame??