Still thinking about this... even ran it past DH at dinner. Love to try and figure out how these little minds tick!

I'd try him barefoot, which should rule out (or in) the shoe thing, though he may be wary out of habit now. Then, though you might look a bit silly, I'd get down to his level and see what it looks like for him. If it is the visual issue, the only thing I can think of is having something in front of him that interrupts his view of the floor. Maybe getting him to carry something in front of him or push a little stroller or trolley.

Would love to hear if you figure it out!