https://github.com/schauder/issue-datajpa-1404-is-null-on-one-to-one/tree/hibernate demonstrates the issue.
Given two entities as follows
The following test fails, because the query returns an empty list:
Making the reference unidirectional going from Parent to Child results in the query resulting in a single result as expected.
This is related to https://jira.spring.io/projects/DATAJPA/issues/DATAJPA-1404
The OP there indicated that DATAJPA-1404 did not appear in earlier versions of Spring Data, but that was possibly not because the query working in Hibernate, but Spring Data using a different query.
Also, since Spring Data generates these queries via Criteria API I expect the same problem also to occur when using the Criteria API to construct an equivalent query.
Looks like the issue is already known.