Open the decsadm.nsf. Go to Activities -> By Type, expand the Replication twistie, and open the Replication activity in question. At the very top of the activity document, under the name, you'll see two columns labeled Source and Target. If this is Keyed Replication (as in, not timestamp), you'll see a column of checkboxes under Target. Skip Insertions, Skip Updates, Skip Deletions. Are any of these checked off?