one
This phenomenon is not directly related to the temperature, it is likely that the screen line has welding or contact is not good, the most likely or the screen is damaged by external pressure, usually large screen mobile phones often because of squatting in the trouser pocket is squeezed, or encounter hard items and damage.
two
It is possible that when there are lines, you try to squeeze the position around the screen, which may disappear, but the most fundamental solution is still to start on the screen, that is, to replace the screen