This is a workaround for Prompt List issue where is shown in wrong position at point of trigger.
The prompt list will display at bottom-left of screen when trigger at the point when the mouse pointer is on the right side or bottom side of the screen.
To resolve this, can just move one pixel away of mouse position from the side prior to showing the prompt list and the list will show in center as normal.
Basically for any case where Keyboard Maestro uses the current mouse screen, if the mouse is on the very right or bottom edge, then it appears off all screens and so Keyboard Maestro uses the wrong location.
This has nothing to do with the Prompt With List action per se, it is just a bug in how Keyboard Maestro maps the current mouse location to a screen.