UI navigation inputs partially not working

I have a UI menu that I've put together with a variety of elements (buttons, toggles, etc.) located on a grid. All elements have explicit navigation set up and point to their appropriate neighbor. All elements have an appropriately sized selection/bounding box.

Using the Left and Right arrow keys for navigation works, but Up and Down do nothing.

Additionally, moving the mouse around the screen highlights semi-random elements (seems to be reversed vertically along with only selecting items in the top half of the screen) but clicking on an element directly triggers the element's action.

I'm using Unity 5.6.2xf1Linux if that helps. This was not an issue until today and an identical menu in another project works fine. Anyone run into something like this in the past?