Hi,
There is a basic conflict going on between what you want to do and the developer's vision of the lesson module. What is the goal of asking students 4 of 20 random questions?
Sometimes a quiz is easier than a lesson for this sort of thing. You can set up a question category with your 20 questions, then have the quiz pull 4 random questions. If you need to put 1 or 2 pages of content or comments, quiz has an information page that you can insert. All the conditions you want on your second lesson can also be set as a condition of taking the quiz.
The orginal purpose of a lesson was to guide a student though materials based upon the student's choice. A student's choice leads (via the jump assigned to it by the teacher) them to a part of the lesson that was appropriate to their choice. So in theory, a student who misses the correct answer goes to one place and the student who selects the right answer goes to another.
Random questions in my mind, allow the lesson to be taken more than once with a high probability that a different question will be selected. It keeps the lesson fresh and perhaps allows discussion because different students maybe asked similar, but not identical questions about a particular point.
The goal of asking questions is really important here. You couild set up 4 clusters, with 5 questions in each cluster, selecting a random question in each cluster. All answers could be graded but all answers would jump to the next cluster. That is the only way I know how to do it in any kind of a lesson. Sounds like you tried something like this.
I have designed a Lesson so that at the end it asks 4 core questions about the content, then picks a random question from a cluster of questions. Had I wanted to increase the probability that every lesson attempt would have a greater number of diverse of questions, I would add more clusters.
I have created Lessons that are glorified PowerPoints, where the purpose of the question is to make sure they read the material. In other words a speed trap. Their "ticket" sends them back in the Lesson , a right answer moves them along to the next content page. They have to get a certain percentage (and only 1 chance at any lesson question) before they can proceed in the course. Often a Quiz is the real test after a few lessons which they must pass to get their certificate.
Ultimately you have to be clear about the goal of asking questions and how they interact with the content.
Sorry to go on about this. It is an excellent "how do I" question, and my answer is also for others who may have the same problem. Glad to see another 2.1.x user.
Hope this helps Chris