Why Grease Pencil will only let me draw a circle around a red dot? - 2.8 Out of the blue this red dot appeared on my canvas. And when I try to draw, the only strokes I can do are those around the red dot, making a circle around it. I can draw near or far from the dot making a big or large circle. Nothing else!
If I use a different tool, like the Fill, or the Eraser, the red dot goes away.

What could I have inadvertently activated?
Apparently I switched on guides by accident...