So, spent substantial time on this, experimented a lot, changed the HDMI cable etc.
Problem with ARC persists, native apps on TV such as Netflix and Prime are not working fine. The sound through ARC drops, especially when the video is paused and played again. Have to toggle the source input on AVR to get sound, especially content with 5.1 surround sound. Don't have any such issue when using Firestick, though its only contained to Dolby Digital.
Noticed another interesting flaw with this TV. Speed of internet at times is slow, this despite the fact that I have connected this with a LAN cable to a gigabit router. At the same time the firestick has been working fine.
Have read plenty of posts, blogs on other forums and sites. All point out there seems to be the problem with TV, especially poorly executed ARC implementation.
I will be putting a formal complaint to MI now.
TBH, extremely disappointed with this poorly engineered TV. The OS is utter useless on this TV. No doubt the display is really awesome. No complaint on that area. The best use of this TV is as a dumb display only, however with poor ARC implementation, even that is not pleasing