I've added Hibernate multi-tenancy to my persistence unit and I started noticing weird results from Hibernate Search queries and then I've identified this log:
INFO [org.hibernate.search.backend.impl.lucene.works.IndexUpdateVisitor] (Hibernate Search sync consumer thread for index it.saiv.oss.common.model.entity.Person) HSEARCH000249: Cannot do fast deletes on index 'it.saiv.oss.common.model.entity.Person'. Entities in this index are conflicting or the index can accept unknown entities.
So I set an indexBase on my persistence unit and I noticed indexes are organized by class, so maybe different tenants are clashing on the same indexes for each class.
This is the relevant part of my persistence unit properties: