Maybe state what version of Lectora you are using? Post a sample file here that shows the error? I believe Lectora incorporates an Internet Explorer COM object, so Internet Explorer version might matter, but the Trivantis team can comment on that. I assume the lines work right in a browser preview. Have you tried different browsers? Do they appear in a published course?
I’m noticing the same thing, but with reflections on objects. The reflection is there in edit mode, but preview or run mode, they’re not there. I wonder if it’s that they need to be ‘rendered’ and will show when the course is published. A bit of a nail biter for sure.