For me, a "crisis of faith" is when ego gets rowdy.
Ego is that vulnerable part of the self that is part of the physical universe. It is the "false self." It is based on action-reaction, so it can be "hurt."
My most recent "crisis" involved a passage in the Bible which said that if you treat others unkindly and you say you love God, you are a liar. In my own moments of weakness, I have been unkind to others. I have allowed my own frustrations to rule me. So, I had found myself to be a liar. That hurt. But it also proved to be an opportunity to clean up a dark spot I had missed. And there are so many left to clean up. I can only welcome each opportunity.
But my favorite definition of "faith" makes "crisis of faith" into an oxymoron. If one has the faith (100% or perfect) confidence that Peter had to walk on water (even though it lasted only a few moments), then there is no room for doubt or "crisis." This definition of "faith" is not found in the dictionary, likely because few have ever experienced it. I have, and it is the most beautiful state I have ever experienced--one I would dearly love to make permanent.