Make sure to autogenerate score serialization hints in a planning solution as defined in OptaPlanner documentation https://github.com/droolsjbpm/optaplanner/blob/master/optaplanner-docs/src/main/asciidoc/Chapter-Integration/Chapter-Integration.adoc. This is required in order to unmarshall the score in KIE server correctly.

XStream:
@XStreamConverter(HardSoftScoreXStreamConverter.class)

JAXB:
@XmlJavaTypeAdapter(HardSoftScoreJaxbXmlAdapter.class)

Jackson:
@JsonSerialize(using = ScoreJacksonJsonSerializer.class)
@JsonDeserialize(using = HardSoftScoreJacksonJsonDeserializer.class)