ERROR: duplicate key value violates unique constraint (Key already exists) - sql

Question

I have this error:
duplicate key value violates unique constraint "HDPL_COMPOSANT_pkey"
Détail : Key (composant_id)=(766975) already exists.
nextVal is superior to MAX(composantId) so why does it show this error?
#Entity
#Table(name= ""HDPL_COMPOSANT"",schema="hdpl")
public class ComposantEntity implements java.io.Serializable {
#Id
#GeneratedValue(strategy=GenerationType.SEQUENCE, generator="composant_id2")
#SequenceGenerator(
name="composant_id2",
sequenceName="\"HDPL_COMPOSANT_composant_id_seq\""
)
#Column(name="composant_id", unique=true, nullable=false)
private int composantId;
#Column(name="code_app", nullable=false)
private String codeApp;
#Column(name="libelle_app", nullable=false)
private String libelleApp;
#Transient
private String typeModule;
CREATE SEQUENCE HDPL_COMPOSANT_composant_id_seq;
CREATE TABLE hdpl."HDPL_COMPOSANT"
(
code_app character varying COLLATE pg_catalog."default" NOT NULL,
libelle_app character varying COLLATE pg_catalog."default" NOT NULL,
composant_id integer NOT NULL default nextval ('HDPL_COMPOSANT_composant_id_seq'::regclass),
CONSTRAINT hdpl_composant_pk PRIMARY KEY (composant_id)
) WITHOUT OIDS;
It crashes when i call this method
#Override
public void createComposant(String codeApp, String libelleApp) {
ComposantEntity composantEntity = new ComposantEntity();
composantRepo.deleteByCodeAppAndLibelleApp(codeApp, libelleApp);
composantEntity.setCodeApp(codeApp);
composantEntity.setLibelleApp(libelleApp);
composantRepo.save(composantEntity);
}
when i try to save my composantEntity it crashes showing the error above
My question is why my Id doesnt take nextVal and take an other value that already exists
am trying to migrate to JPA this method here s the ancient code that i tried to change using the method above
#Override
#MethodLog(logLevel = StandardLevel.DEBUG)
public long createComposant(String codeApp, String libelleApp) {
final KeyHolder idHolder = new GeneratedKeyHolder();
final SqlParameterSource params = new MapSqlParameterSource().addValue(CODE_APP, codeApp).addValue(LIBELLE_APP,
libelleApp);
// suppression des anciens
jdbcTemplate.update(DELETE_COMPOSANT, params);
// creation des nouveaux
jdbcTemplate.update(CREATE_COMPOSANT, params, idHolder, new String[] { "composant_id" });
return idHolder.getKey().longValue();
}