This looks like one of three things :
# Assuming that the display is lit with LED’s, it looks like one or a couple LED’s burned out.
# It could be a locked or stuck pixel , to which I would use UDPixel to run the undead pixel dot at a space of 5x5 and move the flashing dot where the spot is for a few minutes.
# Finally, it could be a dead pixel with no real solution, and you can either accept it, or look into replacing the monitor.
All of this is given without any guarantee of fixing the issue, and is my personal opinion.