@q70007, I don’t know the reason for this, but would say that you’ll most likely need to approach it as all other new vocabulary - with a lot of repetition and patience!
Personally, I would really not try to memorize them under this logic of groups, i.e. I wouldn’t focus on the form, but on the function, learning and practising each word as needed in its respective context. For example, when learning animal vocabulary, I would then work on memorizing words such as galo, gato and gata (with the last two simply being the masculine/feminine versions of the exact same concept). Similarly, I would only worry about words such as gola and malha when learning about clothes, and so on. This should also trim down the number of words you’ll truly need to worry about, because some are not commonly used at all. Moto, for example, is only standard in Brazilian Portuguese - we prefer mota in Portugal.