Bug – Magento 2 Mini Cart
There is currently a mini-cart bug in the latest release of Magento – at time of writing which is Community Edition 2.1.2.
What is it
When you add an item to your cart from anywhere on the website, be it a listing page, product page or widget, the mini-cart will not update.. regardless of theme (Luma, default, 3rd party carts that use the default cart templates). However your Magento store will confirm the item was added to the cart in the green message bar:
Who does it affect
This bug should only affect developers who are running their development environment without caching enabled. Yes, you read that correctly. When you disable cache, the mini-cart does not update as expected.
The obvious as described above is to enable all the caches.
Long term fix
I have been following this issue for a while now without any indication of an official fix being released. Here is the bug on Github
Somebody has applied their own hotfix but that has not been tested or committed yet: