Ecommerce product navigation has slow response time or doesn't response correctl

Hi there! our nav menu found here http://ofdist.wpengine.com/shop responds incredibly slow when clicking a category like “Tables” or “Seating” or “Office Desks” — any of them, really. At times we can’t see that it’s loading anything. For example, you will be in the Seating catgeory http://ofdist.wpengine.com/category/seating/ and when you click http://ofdist.wpengine.com/category/tables/ it will beegin loading that link, but it will then change the link in the URL bar BACK to http://ofdist.wpengine.com/category/seating/. However, sometimes if you wait long enough, the correct items will show up. How can this be fixed?