Copy the example datasource into something like

<datasource jndi-name="java:jboss/datasources/18DS" pool-name="18DS" enabled="true" use-java-context="true">
<connection-url>jdbc:h2:mem:test;DB_CLOSE_DELAY=-1</connection-url>
<driver>h2</driver>
<security>
<user-name>sa</user-name>
<password>sa</password>
</security>
</datasource>

The datasource is not parsed correctly and gets deleted when refreshing using the console.