To force synchronization, log into your server that has the Directory Synchronization tool installed. Open up PowerShell and navigate to C:\Program Files\Microsoft Online Directory Sync. Then start the Directory Sync Configuration Shell by typing.\DirSyncConfigShell.psc1
This will launch the Directory Synchronization Configuration Shell. Once this is open you can type the following command to force synchronization:
After this is done, the online portal will show that synchronization has completed recently.
Note that all synchronization events can be found in the Application Event Log on the server that the Directory Synchronization Tool is installed.