I have some trouble with updating products quantity in cart. When I change qty in the mini cart and click update, nothing happened.
I saw a similar problem in Magento 1.9 and there were answers to add something to the cart.phtml, adding some form-id etc. But I have that in updatecart.phtml and it doesn't fix my problem in Magento 2.
Here is issue: https://github.com/magento/magento2/issues/6656