(Quoted from Keith Stevens, International Coatings. Full article here.)
Over-Flashing: Printers often refer to ink “drying in screen” when it becomes hard and clogs the screen mesh’s open parts. This usually is caused by using excessive heat during printing, most likely after the flashing process. If the ink isn’t given enough time to cool after flashing, laying the screen down on top of the heated print could partly cure the ink it contains, thus clogging the mesh.
Click here to read the full article