@Optimus
On my K2 Plus a fan stay on no matter how long the printer has been at idle… even hours later. The fan is loud, I suspect it is the power supply fan since the fans for model, side, back are all off.
Is this a firmware bug or Creality Print slicer bug?
Most definitely PSU fan. I have 6 printers from 3 manufacturers and all of them the PSU fan stays on all the while the printer is on, even at idle. I have increased fan size on a couple of printers to make them quieter but that is about all you can do.