Just fired up my NOW 4K Smart box and when pressing the signal info button on my TV remote watching NOW it did say Audio PCM where in the past it was saying Dolby D+.
I updated the software in the box Settings and running version 11.5.3 build 4077-68.
All the Audio options in the box Settings are set to Auto.
One thing I noticed on my box was that pressing the star button on the remote the Volume Mode had changed from Off (which I always used in the past) to Leveling.
Set the Volume Mode back to Off.
Since changing the above and going back into the Audio Settings on my box and toggling to the different options back to Auto, the signal is now displaying Dolby D+ again for me when pressing my TV remote signal input information.
I did a power restart and it's still kept Dolby D+ for me.
There is a small lag when navigating around the NOW Home screen and jumping around different page GUI, but it wasn't has bad when the new layout with the gear wheel icon (top right of home screen) when this newer layout was brought out by NOW a couple of months ago.