Crashes while using extended CharacterMovementComponent

is correct!

For others, and for future reference, I made a wiki on this subject a while back here:

Wiki: Custom Character Movement Component

 **Note On Subclassing / Blueprinting C++ Class** Be careful when subclassing a C++ class that uses this structure, **you can't change the custom movement component later** without having blueprinted versions of this class completely freak out. Since you usually blueprint character C++ classes, this is an important precaution to remember! Rama