Upfront draggable elements seem to "hang" and never offer options/settings

After dragging an element into a theme on the front page of the root site (multisite setup), the element seems to hand and I am not able to select options/settings. Once on page, the elements cannot be deleted. Even if the region the elements were dropped into is deleted, the elements remain.

After exiting Upfront and viewing the page, widget rendering errors are displayed on-screen. See the screenshots.