How can we reconcile the warnings issued by some contemporary scholars regarding the presence of flaws in certain individuals, despite their methodology and creed being Salafi, with the acceptance of books from Ash'ari scholars such as Imam al-Nawawi and Ibn Hajar al-Asqalani, despite their Ash'ari creed?

If you know that the shaykh adheres to the creed of the Salaf, then strive to seek knowledge from him and accompany him. The fact that he makes mistakes does not necessitate boycotting him, declaring him an innovator, or warning against him. If every scholar who erred were to be boycotted, then knowledge would not be taken from anyone. Al-Dhahabi said: "And if, every time an Imam erred in his ijtihad regarding individual issues—an error that is forgiven for him—we were to rise against him, declare him an innovator, and boycott him, then neither Ibn Nasr, nor Ibn Mandah, nor those greater than them would be safe with us." It is recommended to consult the book "Classifying People Between Conjecture and Certainty."