searchSimilar in Spring-Data Elasticsearch tries to utilize Elasticsearch's features for searching similarities. But Entities have to be correctly mapped for this to work in query creation. Some of the Fields or Relationships particularly the @OneToMany, @ManyToOne or @ElementCollection saved in Items are relational and so incompatible with Elasticsearch as experienced for itemindex especially if mismatch vs what Items have.Notes regions that facilitate search similarity-related queries may be missing or incorrectly mapped within our index.Let’s consider improving support for searchSimilar and the manner in which the index mappings are defined. Otherwise, things can be properly. If you use "JpaRepository" and "ElasticsearchRepository" together, there may be conflicts. If an entity's lifecycle is different in these repositories, it may cause errors when saving or searching. Thus, it's key to keep the repositories separated with only the necessary operations delegated to each.