After creating a child task in the Planning Console for a project, it might not be possible to move it up or down; the page stays on a loading page and never saves.
While no errors are logged on the System Logs, the following error can be seen on the browser console:
TypeError: Cannot read property 'isAfter' of undefined
at PWGanttTask.eachParent (js_includes_gantt.js:19023)
at refreshParents (js_includes_gantt.js:22847)
at refreshData (js_includes_gantt.js:22833)
at ClientSidePCService.executeGantt (js_includes_gantt.js:22385)
at eval (planning-console.js:172)
at Scope.$broadcast (js_includes_sp_libs.jsx?v=06-05-2020_2026&lp=Tue_Jun_16_20_17_52_PDT_2020&c=24_785:14925)
at deleteHandler (js_includes_gantt.js:14256)
at Object.callback (js_includes_gantt.js:14273)
at Scope.ok (js_includes_gantt.js:25477)
(anonymous) @ js_includes_sp_libs.jsx?v=06-05-2020_2026&lp=Tue_Jun_16_20_17_52_PDT_2020&c=24_785:12321
Release or Environment
Some Project Tasks that are in Closed Complete state have an empty 'Actual End Date' [work_end].
Such Project Tasks should be amended by adding a value for their 'Actual End Date' [work_end] field.
Please note that updating this field from the front end might not be possible; if that's the case, such records should be updated via background script or export/import XML.