Try to switch place on the two GPU, the problem is most likely that the GT 710 do have a lower address value and blender find it before the 760. If that isn't enough it might help reinstalling them and in the worst case you can try to uninstall the 710 and hope that blender prefer a GPU with Nvidia/AMD drivers.
If you are really unlucky it can be that the serial number or address name is screwing with it and can't be solved without editing the code.
I'm more or less 100% on that it is a problem caused by the address name because the GT 710 is GPU 0 in task manager and is more likely to be used than GPU 1.
I have actually never had this problem but the solution is to make the better GPU the one with a lower number.
(You might be stuck with how it is depending on what motherboard you have and how windows react on changes, it is possible that windows will keep calling the 710, GPU 0 because it is registered as it once)