With V1 > V2 I think the Op amp is just going to its lower limit and sitting there. The design is intended to have V2 > V1.
The 10K voltage divider resistors by the shunt, probably want to measure those and see how far out they are. I'm too tired to think how having 5% off might affect things for instance. V1/2 should not be higher than V2/2 if V2 is > V1.
Use R3, R4 20K for a gain of 2.
I'm off to bed ...