Switch to another instance, also open Contacts app (such as http://localhost:8180/magnoliaPublic/.magnolia/admincentral#app:contacts:browser;/:treeview: ) and make sure that your created one was there (after synchDelay=2000 miliseconds)
Clean up your Journal
This is important to prevent your database to be overloaded or hang. Thank you Jordie Diepeveen for reminding us about this.
The journal can potentially become very large. By default, old revisions are not removed.
We recommend turning on the janitor functionality for clusters:
Reference to Magnolia Clustering - Cleaning the Jackrabbit journal and Apache Jackrabbit Clustering - Removing Old Revisions recommendations for more details.
Have a good day!