What is Judaism’s opinion on people who have a ‘Crisis of Faith’? Does this concept exist in Judaism? Why or why not?

Shalom, Thank you for your question. It is not so clear to me what exactly you refer to with the term “crisis of faith”. Perhaps you mean doubts as to the truth of living according to the Torah, or belief in G-d Himself. This is not a “concept” in Judaism, but rather a reality that many people experience. We find even great people in the Bible who “questioned” their faith, in some level or another. Read about Moses striking the rock, about Job, and about Avraham's arguments with the L-rd. To experience a weakening of religious feeling and emotion; a doubt or question; is perfectly normal and common. The question is what does one do with this? The Torah teaches that in such a situation one should continue to serve Hashem by keeping His laws, by continuing to study His Torah and try one's best to connect to Hashem through prayer and good deeds. Even is one is met with silence – one should continue in their labor, with the knowledge that only by maintaining a healthy Jewish soul will they have a chance to be able to connect again in a revealed way with Hashem when he so chooses to reveal Himself to them again. Many is the time that Hashem has hidden Himself from us as a nation – yet we continued to remain His people, and eventually He called out again to shows His love for the Nation of Israel in a revealed way. So too with an individual – even in the dark times when a person feels no connection to G-d or His Torah, one should strengthen themselves with the knowledge that by continuing their efforts towards Hashem, they will, please G-d, merit to again experience His light and closeness. Blessings.