The Elytron applicationKS uses a different type to the legacy realm.

            <security-realm name="ApplicationRealm">
                <server-identities>
                    <ssl>
                        <keystore path="application.keystore" relative-to="jboss.server.config.dir" keystore-password="password" alias="server" key-password="password" generate-self-signed-certificate-host="localhost"/>
                    </ssl>
                </server-identities>
                <authentication>
                    <local default-user="$local" allowed-users="*" skip-group-loading="true"/>
                    <properties path="application-users.properties" relative-to="jboss.server.config.dir"/>
                </authentication>
                <authorization>
                    <properties path="application-roles.properties" relative-to="jboss.server.config.dir"/>
                </authorization>
            </security-realm> 

            <tls>
                <key-stores>
                    <key-store name="applicationKS">
                        <credential-reference clear-text="password"/>
                        <implementation type="PKCS12"/>
                        <file path="application.keystore" relative-to="jboss.server.config.dir"/>
                    </key-store>
                </key-stores>
                <key-managers>
                    <key-manager name="applicationKM" key-store="applicationKS" generate-self-signed-certificate-host="localhost">
                        <credential-reference clear-text="password"/>
                    </key-manager>
                </key-managers>
                <server-ssl-contexts>
                    <server-ssl-context name="applicationSSC" key-manager="applicationKM"/>
                </server-ssl-contexts>
            </tls>