Once the melt layer has reached some critical thickness, frictional heat can no longer be generated, and the melt begins to quench and crystallise thus again increasing the melt's viscosity and begins acting as a viscous brake to sliding.
The process described involves the melt layer reaching a critical thickness where frictional heat generation stops, leading to cooling and crystallization, which in turn increases the melt's viscosity and acts as a viscous brake on sliding.