The fix is to sell both your cards and get a single more powerful card. I've been there, I did SLI a few times back when it had a lot more support from Nvidia and it still was never "good" in terms of compatibility, and things have gone way downhill for multi-GPU support in the last few years. If you can get it to work at all then you know it works, but very few games support it these days. You don't see any muti-GPU benchmarks being included in any hardware reviews anymore.
The post above suggest it's a PCIe bandwidth issue but this is for sure not the case. Multi-GPU does not need dual 16x PCIe lanes to work and having a motherboard that can do that would make barely any difference at all even in the best case scenario.
i7 7700kK @4.2ghz
16GB DDR4 3200mhz
GeForce 1080 Ti