i kind of got round it. i refreshed the pc, so put everything back as was just after upgrade.

i moved the pc to a OU with no gpo's on it. then attached it to the domain and everything remained...

did you ever solve this? i'm having the exact same problem.

pc is fine with W10, then as soon as it's attached to the domain, cortana, start menu and search all fail.

i've tried sfc and dism...