The mentioned error occurs when upgrading from 3.2.6 to 3.4.0. It's clearly related to @Any associations, but I have no clue what the error means. Hence no idea about a solution either. :-)

I've made it a ticket because it's according to 3.4.0's documentation and it works for 3.2.x. All the details are in there (code samples, stack trace, ...).
https://hibernate.atlassian.net/browse/HHH-8858

Is there a kind soul in here who can give me a clue, hint or anything at all of what I might look to next ? :-)

Many Thanks Indeed