Resteasy in EAP 7.1 has got disabled by default
org.jboss.resteasy.plugins.providers.SerializableProvider

So if there is used with application/x-java-serialized-object media type like

 @Produces("application/x-java-serialized-object")
 @Consumes("application/x-java-serialized-object")

and you need to use it, you need to put that provider into
META-INF/services/javax.ws.rs.ext.Providers file

but warn user that it is Security issue to use it.
link http://docs.jboss.org/resteasy/docs/3.1.2.Final/javadocs/org/jboss/resteasy/plugins/providers/SerializableProvider.html