Woo-HOO! Finally working for me! Here's what I did:
- On Mac iTunes, Updated Genius, then Updated iTunes Match
- On iPhone, turned off Match, restarted iPhone, turned Match back on.
At this point, I had Genius (working well so far) but no Mixes.
- On Mac iTunes, Updated Genius, then Updated iTunes Match
- On iPhone, turned off Match, force-quit Music.app, restarted iPhone, turned Match back on.
Still no Genius Mixes. Then, I read the help files again, and saw this note about Mixes when Match isn't on: "Genius Mixes are synced automatically, unless you manually manage your music..." This references the 'Sync only checked music and videos' checkbox in iTunes. On a hunch, I tried turning that off on mine (even though it has no effect, since I'm using iTunes Match). Then I did a sync of the iPhone to iTunes, via cable.
And it worked!!!
Hope that helps someone! Try turning off the 'Sync only checked music and videos' checkbox in iTunes.