Variations error

Hi there!
I have a huge problem for last few days with variations on WooCommerce.
Some products have around 20 variations. In beginning there were no problem, but suddenly one day variations in front end stopped working caused by JS error:

Uncaught TypeError: Cannot read property ‘product_id’ of undefined
– add-to-cart-variation.min.js?ver=2.1.8:4

When you choosing a variation on front-end in drop-down menu, nothing changes (No SKU, no Price, add to cart button doesn’t show), i mean nothing happens when you swapping between vars.
And button “Clear selection” always stays on, even if there no selection on dropdown.
I found a lot topics where people were discussing this problem. I tried so many things, and actually i found one solution which helped me. It was to copy code from add-to-cart-variation.js and paste it inside add-to-cart-variation.min.js with replacing everything.
It helped me, but a got another problem in this case. When you adding product to cart, page refreshes, but it doesn’t add it to your cart.
Does anyone know how to deal with it? It’s really irritating, i spend few days now, and no results..
Thanks a lot in advance, hope to got some solutions here…

WC Version: 2.1.8
Theme Name: Mystile
Theme Version: 1.3.0

https://wordpress.org/plugins/woocommerce/