What is the reason for a student's declining academic performance, their inability to study and revise, and their failure in most subjects? Is this due to low morale or weak faith?

You must search for the cause of your shortcomings in studying and neglecting your duties so that you can address it. This could be due to being preoccupied with other matters, such as excessive television and device viewing, going to the cinema, staying up late and engaging in long discussions, or thinking about matters like earning money and marriage before their time. The reason could also be overconfidence in your knowledge, your specialization not suiting your inclinations, or perhaps the evil eye of envious people. You can refer to your previous state before these changes, and the cure for envy is mentioned in Fatwa (definition) No. 31657. As for weakness of faith, its treatment is obligatory for a Muslim, whether it is the cause or not, and ways to strengthen faith are mentioned in Fatwas No. 42415 and No. 42766.