Issue Summary

When moving a page using the Move option from the ellipsis button at the top-right, by tapping a page that has a lot of child pages, it will keep spinning and not show the children.

After tapping the page again, a "We've hit a snag" error is displayed, closing the dialog.

Steps to Reproduce

1. On a page, tap the ellipsis button at the top-right and select the Move option.
2. On the dialog displaying the page tree, tap a page that has a high number of children.
3. After noticing it spinning, tap the page again while on the dialog.

Expected Results

The page within the dialog should display the child pages.

Actual Results

It only spins and upon being clicked again, an error message is displayed. On the browser's console, the following is displayed:

Uncaught (in promise) TypeError: Cannot assign to read only property 'hasSyntheticChild' of object '#<Object>' at Ee.expandPage (PageTreeController.tsx:672:40) 

Workaround

If the pages are in the same space, manually move them using drag and drop through the sidebar.