Problem with aop subtractor with simple power supply
The trouble with the LM324 is that if you are taking any significant pull-up current you get 0.6 volts or higher as the minimum voltage the output can drop to: -



And I bet you are thinking reading this "but I'm not taking any pull-up current". Well, in fact you are - the negative feedback resistor and input resistor to your "V2" signal are pulling-up the output. The two series 8.2 kohm resistors are pulling the output up to V2 and possibly forcing over 100 uA into the output.