Windows 10 Version 2.8.6.4 Right click on StrokesPlus in window tray > Draw Gestures is selected In preferences: blue color is selected, width 5 pixels.. changing it to 20 makes no difference.
Well, one pattern is that the line *only* shows on my primary display laptop screen: any other monitors I am using do not display the line (doesn't matter which display I make the main one)!
By chance do you have different scales (%) set for each display under "Settings / Display / Scale and layout"?
In a multi-monitor environment, S+ seems to use the main display's scale for every monitor. So if the main display is 100% and another is set at 200%, the 200% display will have the line drawn far from the mouse (direction depends on the scale and display arrangement position). In the case of the main display being set to 200% and another set to 100%, things get even weirder, like drawing the line off screen.
If you are using different scales, try setting them all to the same scale.