I’ve created maybe 100 objects without problem. Yesterday I added 3D text to a new object, but after a few manipulations of the text I found the pencil tool would not create a line on an existing surface. Same result with the rectangle, but the circle continued to work. I closed the drawing and opened a new one. Same problem. I closed Sketchup and then reopened Sketchup and opened an old (and different) drawing. Same problem.
To be clear, the tools work for a new object in a clean, empty design, eg, draw a new line. But after the first line is created, the line tool will not draw a new line that is connected to, crossing, or touching an existing line. But it will draw a new line in open space.