If i reorder a Page and hit the Button "Save Changes" i get the following error:

jabbascripts.js?v=2.8.7:10 Uncaught (in promise) TypeError: Cannot read property 'length' of undefined at PageTree.<anonymous> (jabbascripts.js?v=2.8.7:10) at PageTree.<anonymous> (johnny-deps.js?v=2.8.7:8) at <anonymous>

After refresh of the entire Page, the reordering was saved.