Sorry for my late reply @ptrblck .
Yes, it always stays at 1.0 for ADvsMCI. I trained the same net for ADvsNC and ADvsMCI. The net performed normally on the two datasets, just abnormally on the ADvsMCI. I didn’t tried other models. This is a good way to check and lock problems . I will try it.  I will also check the accuracy for other data sets.
Thank your for these valuable suggestions. I will try them first and then share you the results