there are 2 parameter we need to watch and make sure that replication is running, 1 is Slave IO (the replication engine) and another is Slave SQL,

the Slave IO can  unable to run when we enter the wrong master/ slave paramater like replication user, etc...

 and Slave SQL can unable to run when some sql syntax is replicated to slave but found an error like duplicated key...

 the slave IO still running but when slave sql stopped, your slave will no longer have the same data with your master anymore...

 so you should add another parameter to check Slave_SQL_Running running or not

 best regards