Product review (5 stars): your optics are bad. Hilariously
Yup, that did it.

Tip: If you're not sure whether this is your problem, aim your mobile phone's camera at the emitter. You should be able to see the infrared light blinking. If it's not, your optics are bad.

Hilariously, I had this problem 2 months after the whole ice maker failed and was replaced.