If class D amp changes (improves) sound after few hours, I would recommend to see a “hi-fi doctor” :-).
Despite class D amps are running much cooler comparing to AB/A amps, stress conditions on internal connections/soldering/capacitors/etc are much higher than hot A or AB class amps. I’ve seen capacitors “resurrect” after running few hours, closer to 50%/75% normal, despite 30% performance at start!

