Why might a rectifier circuit not behave as expected?
You are overloading your zener diodes.

If a 16-volt zener is rated to handle 1 watt, that means you cannot put any more than

$$\frac{1 W}{16 V} = 62.5 mA$$

through it &mdash; preferably less.

Even when working correctly, your circuit is designed to put

$$\frac{54 V - 32 V}{220 \Omega} = 100 mA$$

through the two diodes.

It would appear that ZD2 has failed shorted, and ZD1 is now handling

$$\frac{54 V - 20 V}{220 \Omega} = 155 mA (3 W)$$

and probably getting quite warm in the process.

A better design would run the zeners at a much lower current, and use transistors to handle the power dissipation:







simulate this circuit &ndash; Schematic created using CircuitLab