When migrating from eZ Publish this error can appear: Intentionally not implemented: Sort clause not implemented for Location sort field with value 6

This is because some sort clauses have been deprecated: https://github.com/ezsystems/ezpublish-kernel/blob/master/eZ/Publish/API/Repository/Values/Content/Location.php#L60-L79

The fix is to replace invalid values (6, 7, 5) in the database in sort_field columns in two tables: eznode_assignment and ezcontentobject_tree.

This is not currently described in the migration or upgrade guides.