When I analyze your circuit I get that your output voltage should be Vout = 7Vref - 6Vin where Vref = 4 V. So if your sensor outputs 4 volts with no current, I’d expect your output voltage to be 74 - 64 = 4 volts. So it seems to me it’s working per design but not per intent.
I think if you replace resisters R5 and R6 with R5 = 120k and R6 = 160k, that will put Vref at about 3.43 V which should give you the theoretical output of Vout = 6*(4-Vin). That’s theoretical mind you!