Individual Product Subtotal won’t update with quantity change in Side Cart

When I make changes to item quantity (whether on the product page or in the side cart itself), the individual item subtotal won’t show an update. However, the subtotal at the bottom of the cart does accurately update. For example, if I have 5 items at $4 each, the item subtotal will stay at $4 no matter what I do with the quantity. The subtotal at the bottom will accurately say $20.