They commonly occur when there is a large variation between cooling speeds of sections of the material as it flows through the mold.
[1] Flow mark causes vary for specific parts and production lines due to the variability in molds, machines, and materials.
A low temperature will have a similar effect as a slow injection speed due to both causing the material to stiffen before the cycle completes.
[1] If the temperature is increased too high, there is a chance to cause a different type of injection molding defect referred to as a burn mark.
[3] The design of a mold is one of the most important factors in correcting defects due to it controlling most of the process.