So I recently bought Mortal Engines and added to my digital mkv library with DVDFab selecting the AC3 TrueHD/7.1 Atmos audio... went to watch it last night and no sound. So I went to my laptop and tried playing it from VLC and got the mlpa codec not supported message... So is mlpa a new codec not supported by many players? Is this something that can be fixed without losing Atmos? Thankfully, it's the only rip I'm aware of in my library right now but this will be a future problem if more and more physical media comes with this format and my Z9X and 3000 can't play it!
Try remuxing the MKV with MKVToolnix - A Codec_ID of MLPA indicates an originally encrypted TrueHD track. Codec_ID should be A_TRUEHD