From JBoss EAP 7.1 Migration Guide:

YAML Provider Setting Changes

In previous releases of JBoss EAP, the RESTEasy YAML provider setting was enabled by default. This has changed in JBoss EAP 7.1. The YAML provider is now disabled by default and must be explicitly enabled in the application. For information about how to enable the YAML Provider in your application and add the Maven dependencies, see YAML Provider in Developing Web Services Applications for JBoss EAP.

Default Charset UTF-8 in Content-Type Header

In JBoss EAP 7.1, the resteasy.add.charset parameter is set to true by default. You can set the resteasy.add.charset parameter to false if you do not want RESTEasy to add charset=UTF-8 to the returned content-type header when the resource method returns a text/* or application/xml* media type without an explicit charset.

For more information about text media types and character sets, see Text Media Types and Character Sets in Developing Web Services Applications for JBoss EAP.

SerializableProvider

Deserializing Java objects from untrusted sources is not safe. For this reason, in JBoss EAP 7.1, the org.jboss.resteasy.plugins.providers.SerializableProvider class is disabled by default, and it is not recommended to use this provider.

A new set of RHAMT Rules should be added to address the app migration issues detailed above. Please let me know if you need further info for the "when"s and "perform"s.