When I create small maximum entropy designs, I get unbalanced distributions for the variables. It's mostly regular and with some extra points at the ends; however, the lower end is sampled much more frequently than any other point. I have tried it many times and attached a few examples to this message. If needed, I can provide more.
As you can see from the screenshot above, -1 is sampled must more frequently than any other value. Even with a continuous distribution it's clear that the lower limit is sampled more frequently:
However, it doesn't always happen. Unfortunately, in my experience, it happens more often than not. I have attached a few designs where the issue appears and disappears.
It is very difficult to assess the design one factor at a time. The solution must satisfy a multivariate criterion. Looking at two factors at a time, still short of all 20 factors, shows a smoother spread of runs.
If you believe that there is a problem with your design, you should reach out to JMP Technical Support (support@jmp.com) for resolution. If so, please reply with their findings and your conclusion.