@GeneratedValue(strategy = GenerationType.AUTO) not working as thought

You may use GenerationType.TABLE. That way, jpa uses a sequence table for id assigment and you may never need to generate sequence or auto-increment values or triggers that lowers portability.

Also note that in java int type is initiated with 0 default, so you may get rid of that also.

In my case it was about bad dialect:

hibernate.dialect=org.hibernate.dialect.H2Dialect

instead of:

hibernate.dialect=org.hibernate.dialect.PostgreSQL9Dialect

when I switched to the production database. Hibernate tried to use strategy prepared for different db engine.

I had a problem with a similar manifestation to yours. I eventually discovered that the configuration of my database connection was wrong: I was connecting to an old database that had an incorrect schema. The new schema declared the primary-key column as

"ID" BIGINT NOT NULL GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1)

so the database itself automatically generated the primary key whereas the old schema declared it as

"ID" INTEGER NOT NULL

Hibernate executed the correct code for the new schema, which failed on the old schema because the old schema demanded the SQL INSERT provide a value for the ID column.