Can you describe what are the symptoms of "gear slipping". Do you often drive your car hard?

FWIW almost 3 years of ownership with the car I believe this Preve Turbo's CVT is not very suitable to be driven hard. Occasionally yes, but not frequently. Not too sure about others but in my experience the CVT will show some anomalies and act weird if it is subject to frequent hard acceleration. Some signs are the CVT showing louder sound even when you drive slow, weird whining/louder sound and a slightly jerky drive.

I still drive the car with frequent burst of acceleration everyday, but not as hard as before. I'm worried about the reliability of the CVT which doesn't seem too robust from the way it is acting now.

And also, how often does the loud some comes up? Does it happen every time when your parents step on the pedal, or it happens on and off, occasionally?

I suspect the Auto Cruise function comes into play.  At 1 time, I had accidentally flicked on the Auto Cruise button whilst turning the steering wheel.  The effect is high engine rpm at low speed. Seems that the automatic gear won't downshift.  I then slowed the car to a stop, switched to "N" and then back to "D".  Thereafter, everything's back to normal again.