An exception looking like the following about a netty issue is thrown when executing Elasticsearch Mappings.
Remove "<stambiaRuntime>/lig/global/netty-all-4.0.0.final.jar" file from the Runtime which is executing Elasticsearch Mappings.
This library is causing conflicts with the netty library used by Elasticsearch.
Removing the one shipped with the Runtime should resolve the exception issue as the Runtime will then use Elasticsearch's one.
Note that for this workaround to work the Runtime must not be the local Runtime included in the Designer, as the Designer resets its internal Runtime libraries at each restart (so the netty library will be recreated at each Designer's restart.)