For content services in cluster, content is stored at a shared location which can be accessed by each node. Only indexes for this content is synchronized across cluster nodes. Please make sure that content storage root directory is a shared and accessible location for all nodes in the cluster.
Could you please perform a quick test?
1. Go to http://node1:port/contentspace and add a content here.
2. Now go to http://node2:port/contentspace and verify that you can see the content added.