getting rid of dc offset at input of unity gain difference amplifier
The DC offset of V2 is blocked by C3, but that doesn't prevent a DC offset from feeding back through the 190K resistor. It may be a very small current, but the plate on the right side of C3 will charge to the average of whatever DC offset is present on the right side unless you bias the right side of C3 with a resistor connected to, for example, ground (which has a 0v DC offset) using a 10k give or take.