High stuffing box pressure can distort a lapped face. Thermal distortion can distort a seal face. The product changed state and is restricting the movement of the seal. The product can crystallize if you change the temperature in the stuffing box. A temperature change or agitation can cause a product to become viscous and interfere with seal movement.
Some liquids can solidify with a change in temperature, pressure or agitation.
A change in temperature or pressure can cause a product to build a film on the seal sliding surfaces. The product vaporized between the faces and blew them open. This can happen with an increase in temperature or a decrease in stuffing box pressure. Solids clogged the springs or some other part of the seal, restricting seal movement. Solids outboard the seal can restrict axial movement as the seal moves to compensate for carbon wear.