I meet many players who struggle to play bunker shots when the ball is buried or plugged. A buried lie is the results of the ball landing in soft sand and then staying is the depression that is left by that impact.
The difficulty with this shot is due to you not having easy access to the back of the ball. This results in less spin on the ball and thus less control over the shot, so you must play it differently to a normal bunker shot.
A normal bunker shot requires a swing motion that results in high ball flights with a lot of spin on the ball. This type of ball flight is just not possible form a buried lie.