2.4V Zener diode regulator not clamping
A 2.4V (@5mA) Zener is going to have a heck of a lot more than 2.4V across it at close to 50mA. Just the way the physics works out for low voltage zeners.
3.3V or so (typical) looks about right.

Use a TL431 instead.
Just as a rule of thumb, think twice about using any zener &lt; 5.1V.