I have a 2015 85D and notice this setting being toggled automagically from time to time. That said, I find the Dolby setting quite random. Some songs sound much different/better with it off than on; and vice versa. Other songs I don’t here a major difference. But I’m not an audiophile.
Edit: this car has the Premium Sound package.
My Dolby Sound has changed to Immersive sound and back again several times over the course of several updates. Currently on 2018.48.12, and it's reverted back to Immersive Sound. The issue I find most annoying is I can't hear any difference between any of the 3 levels in Immersive sound, whereas I could immediately hear a difference activating Dolby Sound. I'm guessing that it is because my 2017 S90D MCU1 doesn't have the Immersive sound hardware and can't react to the options until it is returned to Dolby Sound control programming, but that's just my guess.
Anyone else notice that Immersive Sound is unresponsive when used in an UHFS vehicle originally equipped with Dolby Sound?