It appears that the issue is in the SingleTableEntityPersister, in 5.0.1 it used simple logic to get the table name. As of 5.0.2 and higher, it uses more complicated logic to determine the table name.

https://github.com/hibernate/hibernate-orm/blob/master/hibernate-core/src/main/java/org/hibernate/persister/entity/AbstractEntityPersister.java#L5154

The changes that Steve Ebersole put in for HHH-10133 make perfect sense, so my hunch is that some dialects like MySQL need to be set to use SCHEMA and CATALOG based lookup, to make it consistent with how they may have been used in the past.