[Ameiseuk]

One touch power windows look for an overload current to the motor which occurs when the window hits resistance or its end stop.
The 'lower window and hold the button down' setting sequence allows the sensor to reference this overload current and know when to stop.

If there is an impediment in the process, e.g something jamming the mechanism then the system sees an overload and stops.
It may be that the current sensor has failed or the impediment is very close to the start of a raise cycle.

Does the one touch work if the window is already half open or closed?

Where this occurs depends on the car. On most older japanese cars the drivers window switch has a little circuit card inside that takes care or this. In my old p38 range rover it was stored in the body control module.

Haven't delved that far into audi electrics yet to find out more yet