Does anyone have a clue what the following error message might mean? 'The merge process detected a mismatch while evaluating the subscriber partition validation expression' (SQL Server error #21299)

I am working with SQL Server merge replication. I sometimes get the error when I try to perform a merge between the publisher and subscriber databases. A merge reinitialization will resolve the issue and allow further merge processes to be run correctly.

My system is configured with the following constraints:
1) The publisher creates a new snapshot and dynamic snapshot once a day.
2) The merge process is initiated as a manual step.
3) I am using a dynamic snapshot to filter the data at the subscriber.