Hello Mery, well if you have used the Walk Forward Optimization and you get any of the strategies from the collection, it means that the strategy already passed the Walk Forward Optimization. And you are doing WF optimization on the one that is already optimized.
This is why you do not see a better strategy because you are trying to optimize with WF the one that is already optimized. It is not the original one that you are having in the collection. We do not see the original because it was changed from the WF optimizer.
Hope that helps.