7 files declare their use of ParentCandidateInterface in Entity Reference Hierarchy 3.x

EntityHooks.php in modules/entity_hierarchy_microsite/src/EntityHooks.php

HierarchyChildrenForm.php in src/Form/HierarchyChildrenForm.php

MicrositeCacheContext.php in modules/entity_hierarchy_microsite/src/Cache/MicrositeCacheContext.php

MicrositeMenuLinkDiscovery.php in modules/entity_hierarchy_microsite/src/MicrositeMenuLinkDiscovery.php

ParentEntityDeleteUpdater.php in src/Storage/ParentEntityDeleteUpdater.php

ParentEntityReactionBase.php in src/Storage/ParentEntityReactionBase.php

ReorderChildrenAccess.php in src/Routing/ReorderChildrenAccess.php