@Christian Ciach 5.4.0 actually came with fixes for a lot of regressions related to persisting and fetching OneToOnes, namely HHH-12842 Closed and HHH-12436 Closed which were introduced with HHH-9460 Closed . The only issue regarding one to ones that remained and that we're aware of is HHH-13085 Open , for which Gail has provided a work in progress fix.

Vlad, Gail and I all contributed to the implementation we ended up with in 5.4.0. If there is another use case of OneToOnes that has since stopped working, please provide a test case and file a new issue.