Nested array in Autoform trouble

I have my project running here. I’m having trouble with my ability to add questions.

When you select ‘Numeric’ type of question, I can’t click the ‘+ Units’ button to add a unit.

Code for my schema.js is here. The rest of the code is in the same repo here.

I wan’t to know what I’m doing wrong. I can delete a unit, but I can’t add a new one. Is this a bug in AutoForms?