If all connectors are in the SYNCING state, but modifications are not being synchronized, then verify that the synchronization settings are correct:
Using the Console, verify that the attribute being modified is a synchronized attribute (note: passwords are always synchronized). If created user entries are not being synchronized, then verify that user creation flow is enabled in the Console.
Does the source connector detect the change to the user? Use the central audit.log to determine if the connector for the directory source where the user was added or modified detects the modification. Does the destination connector process this modification?