Office 365 to CRM synchronization issue

Hi Guys,

We have one Production instance of Dynamics CRM Online 2015 Update and another of test/dev instance of Dynamics CRM Online 2015 Update, until now, I could assign 'Microsoft Dynamics CRM Online Professional' licences to any user and that user was appearing fine in Production  & Dev Instance. but somehow, since Friday, we bought two new licences of CRM and assigned these two licences to two users.

The issue is that, those two users does not show in Production Instance of CRM but they show fine in Test Instance of CRM!!?

I tried to re-assign the licences to affected users but no help. Always users appear & disappear fine upon re-assigning users on Test Instance, but never appears on Production Instance.

I cant see if any other settings were changed at all and it was working before fine, not sure if it is something to do with when I bought two new licences but dnt see any problem there either.

those two users are member of same group who are appearing fine in both Instances and I dnt see any difference between users who are appearing fine vs users who do not appear on CRM.

Any help is much appreciated.