If you hide or show more than a few child controls on a form, the show and hide functions intermittently crash. The more child controls you show and hide, the easier this is to reproduce.
The specific error is
Uncaught TypeError: vnode.el is null
As a workaround, I am setting a css class where I need to show/hide items or column/row groups and setting style.display to toggle show/hide those elements when the form is active.