Is all the processes running fine or any processes abended? Check this using.
INFO EXTRACT <EXTRACT_NAME>
INFO EXTRACT <DATA_PUMP_NAME>
INFO REPLICAT <REPLICAT_NAME>
Manager and extract are in running state on both source and target
Ok. Now check where the data sync is getting lost. Like check for total count of DML operations by each processes. Like below.
STATS EXTRACT <EXTRACT_NAME>
STATS EXTRACT <PUMP_NAME>
STATS REPLICAT <REPLICAT_NAME>
As Parth pointed out, you need to find it out. Alternatively, if you know the tables being out of sync then you can run something like below:
select * from T1
select * from T1@dblink;
This will give you the difference of records which you can insert manually. This method is good only for very small amount of data or few tables and not for many tables. If you have issues in many tables then you can remove them from replication and add them back which will bring the table in sync status. Once you do this, keep an eye on these tables and if they go out of sync again then it will be evident that replication is encountering some issues in replication which needs to be worked upon.