Am I missing a secret - any circuit with an Opamp fails

[DiscoVlad]

I assuming that the floaty unused half of the 4558 isn't actually left unconnected.  (Connect - to OUT and V_REF to +.)

Basically this, you need to terminate unused inputs or strange/bad things can happen.

[antonis]

There is no need for 1M resistor grounding unused non-inverting op-amp input..
It can wired directly to Vref or GND (whichever comes closer..)

[DiscoVlad]

Agreed, the 1M is optional.

However, ground on this circuit is a supply rail and opamp inputs tied to either side of the supply is bad - it can lead to latchup/excessive current draw/noise/damage to the chip/etc.