I see different possible reason:
- Network issues: DNS / slow speed (you can configure the update depending the net speed, is this setting done?)
- The gpupdate /force must be run on the client, not on the DC
- You set user level GPo on a OU containing only computers, or the reverse.
I hope it will help you a little bit… (I am not a GPo Guru, I’m more a GPo “normal” user)