JPA Repository.findByKeyEquals() returns not present value, but the value is exist on db - spring-boot

Question

I'm developing an application that queries a database.
There are a few issues right now.
history.isPresent() == false when calling Optional<History> findByKeyEquals() intermittently. but value is exist on database
This is the information I got while tracking the issue.
All child entities are non-null.
In most cases, if the same function is re-executed, it is searched.
But sometimes it doesn't happen intermittently.
i think that i use incorrectly table relationship annotation (#OneToMany,#ManyToOne options..)
I want to solve this issue.
this is my code
History (Parent)
#Table(
indexes = {
#Index(columnList = "key", unique = true),
})
#Entity
#Getter
#ToString
#Audited
public class History implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(updatable = false, nullable = false, columnDefinition = "BIGINT UNSIGNED")
private Long id;
#Setter
#Column(nullable = false, columnDefinition = "CHAR(36)")
private String key = UUID.randomUUID().toString();
#Setter
#Temporal(TemporalType.TIMESTAMP)
#NotAudited
private Date started = new Date();
#Setter
#Temporal(TemporalType.TIMESTAMP)
#NotAudited
private Date finished;
#Setter
#OneToMany(
cascade = CascadeType.ALL,
fetch = FetchType.LAZY,
mappedBy = "history",
orphanRemoval = true)
#NotAudited
private List<Content> contents = new ArrayList<>();
...
}
Content (Child)
#Table
#Entity
#Getter
#Audited
public class Content implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(updatable = false, nullable = false, columnDefinition = "BIGINT UNSIGNED")
private Long id;
#Setter
#Column(columnDefinition = "LONGTEXT")
#NotAudited
private String content;
#Setter
#ManyToOne(targetEntity = History.class, fetch = FetchType.Lazy, optional = false)
#Audited
private History history;
...
}
Repository
public interface HistoryRepository
extends JpaRepository<History, Long>, RevisionRepository<History, Long, Integer> {
Optional<History> findByKeyEquals(final String key);
}