The Draw vertical line from () to length () colour () block is found under the Robotics palette in the extension evive TFT display. This block takes the coordinates of the starting point of a line as input along with length and colour. Starting from that point it draws a line extending downwards. This is a limitation of this block; it can only draw lines (vertical) from a lower Y-coordinate to a higher Y-coordinate and not the other way round.
Remember that a higher Y-coordinate will lie below the lower one since the positive Y-direction is downwards.