I'm a fellow user trying to make sense of what you're seeing. I don't know for certain what is happening behind the scenes. See Apple Music - Apple Digital Masters - Apple. This paragraph from the Apple Digital Masters (PDF) link is perhaps relevant:
Note: Apple Digital Masters replaces Mastered for iTunes as the name of the program to reflect the fact that these audio advantages are available to our entire music catalog across the Apple ecosystem, whether streamed or downloaded. All Mastered for iTunes releases are now badged as Apple Digital Masters and the Mastered for iTunes software tools are still usable for Apple Digital Masters creation.
It may also be worth noting that I've seen at least one user complaining that their (presumably redownloaded) music was now a remastered version when they preferred the original.
tt2