This is not surprising at all to me considering some comments from AMD I can't seem to find, ATM
From my understanding Fury X GPUs have voltage determined individually, so they should all be running pretty close to the lowest stable voltage - so we should expect exactly nothing for overclocking on stock voltage.
As for the memory clocks, it could be a number of factors. Possibly the drivers simply aren't ready for it or, possibly, overclocking HBM brings no benefits, or, worse, damage occurs when overclocking HBM just as or even before any symptoms of instability occur.