Hydrodynamic forces generated between the lapped faces. Pressure distortion caused during pressure peaks such as water hammer and cavitation. A failure to provide equal and opposite clamping across the stationary seal face will cause distortion. A hardened sleeve can cause the seal set screws to slip. A wrong initial setting of the face load.
Springs can clog if they are located in the product.
Loose set screws. If the sleeve is too soft they can vibrate out. Shaft tolerance and finish is out of specifications. The rotating shaft or seal hits something. The discharge recirculation line can force open the faces.