2015 Hyundai Azera intermittent changing gears issue

Hi, 
my name is Maher and I am an Electrician
I’m glad to be part of this community 

One of the car that I’m working on is Hyundai Azera 2015 and the issue is difficulty in changing gears and it’s intermittent, sometimes at high speed, sometimes at low speed, when the issue occurs you can feel the car is vibrating so hard for a second 
I scan the car and there were no codes, so I checked live data and I noticed the gear engaged status isn’t stable at Drive while the car is moving and it keeps changing between D & P,N,R 
so I suspected the neutral switch/ transmission range switch and checked it and found it working fine but to be honest I didn’t check the harness to the PCM 

I think it’s mechanical issue but I want to be sure 
history of the car as per customer: 
He replaced the PCM ( no information about the reason ) and there was an oil leak from the transmission pan and it has been repaired 

I hope that you can help me with this and 

Regards