Ok, can you try the following (just to clear out any potential cached data)..
Fire up your Preview for Developers app and tick the "enroll" button and then check for updates.
Restart the phone (long press on the power button and shut down)
Go back into PfD, un-enroll and then check for updates again.
I know you've done this before, but rotating around the loop might clear some cobwebs out. Meanwhile, I've gone behind the curtain and asked again for an update on why you're not being updated.