Difference between Mach buffet and shock stall
Transonic buffet is caused by the separated turbulent boundary layer striking the airframe (horizontal stabilizer, wings, fuselage) with considerable force causing a high amplitude vibration, which physically shakes the whole aircraft. It's highly destructive and all commercial aircrafts should avoid entering a buffet boundary zone. That's why commercial transonic aircrafts are limited, not only by IAS, but also with Mach number as well. The reason for separated boundary layer is a shockwave formation on the airfoil which causes a great adverse pressure gradient and separates the airflow from the wing. The transonic aerodynamic buffet is an imminent warning to the shock stall. As the shockwave strengthens and separation becomes even more severe there will be a great change in coefficients of lift, drag and pressure. These changes will induce more drag, and due to the Cp changes on the airfoil it will cause mach tuck to occur. Mach tuck is a phenomenon which causes a nose down tendency of an aircraft and it is very difficult to compensate it only with the elevators. When all that occurs then we are talking about a shock stall. Shock stall is associated with an aircraft dive while transonic buffet is a warning sign to the shock stall and physically shakes the whole aircraft with a quite destructive force.