Having recently returned to the cintiq from a long hiatus I had the wavy line issue strike again. And since I know the cause and fix I figured I would share it.
Above you can clearly see the issue. Both of those lines you see were drawn with the same straight line motion. One however (bottom) is horribly wavy! Dear god it’s a fucking mess!
The wavy line shows up when windows turns off the display on the cintiq. Since the cintiq isn’t a normal monitor, it’s more like a tv, hence why when you power it off windows assumes the display is no longer attached. Windows seems to just fuck everything up.
So to fix it after it’s turned off the display you need to power cycle the cintiq. this should restore the lines!
It is however recomended that you simply go to control panel, power management, and set “turn off displays” to “never” to avoid this all together.
TL:DR: Power Cycle the Cintiq and then set window’s “Turn off Displays” to “Never”