MacBook 2015 or MacBook Pro 2016 has an unresponsive key, or a key that feels different than the other keys when you press it
Hold your Mac notebook at a 75-degree angle, so it's not quite vertical.
Use compressed air to spray the keyboard, or just the affected keys, in a left-to-right motion.
Rotate your Mac notebook to its right side and spray the keyboard again, from left to right.
Repeat the action, this time with your Mac notebook rotated to its left side.