This issue can be closed now. Updated "parseListeners" method in Class " org.activiti.editor.language.json.converter.BpmnJsonConverterUtil" by adding below line:
else if (element instanceof Activity) { ((Activity) element).getExecutionListeners().add(listener); }else if (element instanceof IntermediateCatchEvent) { ((IntermediateCatchEvent) element).getExecutionListeners().add(listener); }