I encountered this lag problem too in lesson 6, but now I understand what's going on thanks to your discussion. Thank you!
I think it would be helpful to have an explanation, about the lag issue, at the beginning of the Lesson 6 PDF and at the top of the coding comments for the scene.
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Cheers for the feedback. That was a product of releasing the lessons as I went at the time and having each lesson contained within its own project file certainly caused some problems with the course flow over time. This was one of the reasons why I switched to a single project file from lesson 7 onwards.
In any case, now that the course is complete and I'm working on a GB Studio v4.2 update, I have been able to completely revise the course flow and iron out a lot of these kinds of issues. Lesson 6 has been replaced since P+ is no longer needed in GBS 4.2. The project is set to color mode only and there is only one project for the entirety of the course.