This is an update of my previous post.
After disabled the new player in the Plex player settings, like I already said, evererything works fine back. But it’s not really true. I was able to play video but only in 2.0
This situation reminded me this post:
To solve this previous issue I set manually in Android TV the supported audio format and it works fine.
But since the last android TV update it seems that this manually seetings are the issue. I set back to automatic and now the player including the new one can play well all videos with the right audio format.
Hope this help.