I tried your test case template and it works like a charm !

So i wondered why it was not working on my repository, then regenerating same project as java project showed me it was working in JAVA.

Finally, I found that the problem came from Kotlin and a missing plugin useful for that usecase: all-open.

https://stackoverflow.com/questions/37733629/kotlin-with-jpa-hibernate-no-lazy-loading-without-open

As soon as I configured it, I worked like a charm.

https://github.com/pcavezzan/parent-child-relationship-hibernate-6/commit/32bd028bee9aafd78e143b0cc225fe6af2672b22

Sorry to have bothered you with a none problem. I’m closing this issue.