what problems are created as a result of montags friendship with clarisse?

This depends on how you look at "problems". Clarisse is Montag’s awakening. Everything changes after he meets Clarisse. Montag begins to see the truth about his job and society. His life also begins to unravel. He loses his wife and becomes a fugitive on the run. Mildred says a car, but her death remains suspect, hit Clarisse.