Low-Side Driver Not Sourcing Current from Load to GND

Question

I have a circuit with an electronic load in parallel with an optocoupler and a low-side N-channel MOSFET connected to the circuit. The low-side N-channel MOSFET driver is supposed to source current through the electronic load when activated, shorting the connection between the electronic load, optocoupler, and low-side driver. This in turn activates the optocoupler circuitry to activate an enable signal on the output side of the optocoupler. The problem is that there is a voltage across the connection between the load, optocoupler, and low-side driver of 11.1V with the +12V supply's ground as reference. This leads me to believe that the low side driver is an open circuit and failing to source current, creating a loop of current through the optocoupler and electronic load, but failing to travel through the low-side driver to ground and complete the circuit. The optocoupler is an H11L1M from Onsemi and the electronic load FET is an IRFZ24N N-channel Power MOSFET. What could be causing the low-side driver to fail in sourcing current to the +12V ground to complete the circuit? Node voltages are labelled in diagram below to help in analysis if necessary.