I am facing a similar issue on ASRock x399 Fatal1ty which uses a Nuvoton NCT6779D chip where CPU fan (actually radiator fan) is not showing up when it is not spinning.
The fan is not spinning because it's stopped by firmware as set by me with thresholds in ASRock F-Stream.
Could there be an option to allow showing 0 RPM fans? I can hide superfluous ones later in sensor settings. The fan does show up once it ever spins up.