Analog multiplier using logarithmic and anti-logarithmic opamp issue
The antilog amplifier saturates because it cannot drive the output voltage to the level required to make the current through the feedback resistor match the current through the diode.

To fix this, you either need to raise the supply voltage, or scale the currents down by raising the values of all of the resistors.

Are you simulating with "ideal" opamps or models of real opamps? In the latter case, you may have offsets and bias current issues you need to address as well.