I think the RESTEasy client dependency should be upgraded from 3.0.4.Final to the latest stable one which at the moment is 3.0.10.Final? There have been a large number of bug fixes in between so I think it is good to stay up-to-date.
We use the RESTEasy client in Magnolia for consuming an external REST API so it is important for us to use the latest version. We have upgraded to 3.0.10.Final manually and everything seems to work just fine.
Please Check as well: