Major Description
In Jackrabbit Classic each node, even non-referenceable ones, has a UUID as its identifier, and thus the jcr:frozenUuid properties of frozen nodes are always UUIDs. In contrast Oak uses path identifiers for non-referenceable frozen nodes (see OAK-1009), which presents a problem when dealing with version histories migrated from Jackrabbit Classic.
To avoid this mismatch, the upgrade code should check each frozen node for referenceability and replace the frozen UUID with a path identifier if needed.