I can't explain why the bug happens but I should be able to fix it in a brute force way.
For some reason, your cursor is managing to intersect with an object that does not have an entity associated with it. There may be something related to a tile boundary at play.
... but in general the scene shouldn't have objects that aren't associated to some entity. So I may leave the "bug" and add some more debug for the next time someone sees it.
(Unless I figure out how to reproduce it.)