Optimo - bug with more iterations or population



I am using optimo for finding the best position for a numbering block on a drawing. It works perfectly with 40 of populationSize and 20 Iteration Number. The problem is that I want it to be more precise, but if I try to change iteration number for 30, or 35, or even just try to change the population size for a bigger number, the function does not work… There are some “magic numbers” that work for one of the objects but not for the others, randomly (it looks like)… Can anyone explain me that? I really have no idea of why does it works for some iteration numbers and not for others…
Thank you!