There could be several causes for this, if there is multiple domain controllers it could be a timing and/or syncing issue with AD, or if the computers are having issues connecting to the domain controller they could be using cached credentials.
Can you provide some more details like: 1. How many domain controllers do you have 2. Are there multiple locations 3. Is there any similarities between the users who are not getting the settings (Same location, subnet, device type etc) 4. Operating system version (Servers and Clients) 5. Domain and Forest functionality levels.
Additionally it might be worth checking the event logs on the Domain Controller the effected clients are connecting to and the effected computers themselves.