Currently, I am working on AEM 6.3 to AEM 6.5 upgrade project. while upgrading I noticed that cq:dialog is deprecated or missing from libs page component for both libs/wcm/foundation and libs/foundation/components.
so if you have a cq:dialog in your project page component and extending from libs page cq:dialog using the path property. in this case, your project page component page properties will be broken.
Solution: Delete a dialog from your project page component if no custom tab is present. and then change the sling:resourceSuperType to apps/core/wcm/components/page/v2/page.