V-brake caliper arm not retracting after hard braking When breaking lightly it doesn't happen, however when clamping hard it gets stuck. Whenever I bring the bike to a complete stop I have to manually un-jam it.

Here's a video:
It looks like there's dirt in the hinge. When you brake hard, the arm reaches the dirty region and sticks there, and the spring can't force it back; when you brake more gently, it doesn't get into the sticky region. Detach that arm, clean it and re-lubricate it.