Settings-Watch.bundle not in sync

Hello.

I want to be able to change settings for my Watch app on iPhone as well as from within the app. What I did:

1. Create Settings-Watch.bundle, define groups and individual settings.
2. Add App Groups capability for all 3 targets (iOS, WatchKit, WatchKit Extension)
3. Add group group.com.my.appxyz to every target's App Group
4. Add ApplicationGroupContainerIndentifier : "group.com.my.appxyz" on my Root.plist

Now I can change settings for my Watch app on iPhone, great. Let's access those values from within the Watch app. Loading values:

let settings = UserDefaults(suiteName: "group.com.my.appxyz")

settings?.register(defaults: [
  "something" : sameSensibleDefaultAsInRootPlist,
  ...
])

let something = settings?.string(forKey: "something")

Saving values:

settings?.set("newValue", forKey: "something")

The changes I do on Watch are persisted and properly loaded between sessions, just as expected... Except they never reflect on the iPhone side of things and vice versa.

I've reinstalled the app on the simulator and on real hardware - still doesn't work.

Did I overlook something, perhaps?

Thanks!