I can't see the lines as I draw them over the guide lines of the measuring tape

I am new to Sketch Up and I’ve bumped into a couple of difficulties.

I can’t see a line when I draw it on a guide line made with a measuring tape. I can only see it as soon as I delete the guide line. It seems as if the guide line is layered in front of the line that I’m drawing.
Does anyone know how I can fix this?

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