Sequence number shows a lower value after dump file import
If you run export command against live database without parameters like flashback_scn or flashback_time which ensures consistency during the export, then this can be an expected behavior because these objects are exported in different time and one can become inconsistent with another. 

For example, if the sequence object is exported before the table and the application has inserted new records using the sequence and exported later then table and sequence can be out of sync. 

Stopping application before starting the export process or using expdpparameters like flashback_time(this may not export all the transactions made after the time specified in this parameter unless you stop the application) can prevent this situation. Or you can adjust the sequence value after the import by recreating it.