Finally, my local mechanic sorted it out (for 800$)
Below is what he ended up doing
1. Flush and fill ATF, still the issue did not go away
2. Changed the transmission body valve and the problem went away
He did tell me that he has seen similar issues before on other cars....
Just wondering what could be the issue with these transmission bodies, one of the many valves could be faulty ?
Could it due to usual wear and tear or some faults ?