After a major update Copy Page Tree is not working. The New Parent page options are not loading
Did you perform a major update from a Confluence version prior to 7.X.X?
There may be some issue with the index. Did you reindex after upgrading? How to rebuild the content indexes from scratch
Do you have custom HTML on your pages? (under General Configuration)
Check to see if you have any AJS calls. Some were depreciated between versions. Remove those calls and the app should return functionality.