Why doesn't 'Bite Shoes' trigger the effect of 'Tragedy' in Duel Links?
It depends on what card you changed with Bites Shoes.

Tragedy requires that the monster which changed position from attack to defence, be face-up and under your opponent's control.


If you changed the battle position of a monster you control, this effect does not apply, and no monsters are destroyed.
If you changed the battle position of a defence-position monster to attack position, this effect does not apply, and no monsters are destroyed.
If you changed the position of a face-down monster, this effect does not apply, and no monsters are destroyed.


If you changed the battle position of a face-up attack-position monster that your opponent controls, to defence position, then the effect should be activated. Only in this case have you found a bug.