SQL Server Merge Replication Dummy Update issue
We have found a lot of records in MSmerge_metadataaction_request pointing to the same article (table), in action = 5. 

They look like garbage. When profiling the database those records are returned to the working process even though the article was not included in the subscription that was running (another subscription).

Deleting the records from MSmerge_metadataaction worked out. However, I am not sure if that will generate issues in the long run, at least now the subscriptions are synchronizing.