Jeroen,
When the cart contains an item with free shipping and you have one or more items that should have shipping charges, the cart is giving free shipping to everything when you check hide other methods.
If you don't check hide other methods, the customer gets a choice of paying shipping (which is the proper amount) or free shipping.
Of course they are going to choose the free shipping every time.
Is there a way around this problem?
Thanks,
Ed
https://wordpress.org/plugins/woocommerce-advanced-free-shipping/