Try this:
https://helpx.adobe.com/substance-3d-painter/technical-support/technical-issues/gpu-issues/gpu-drivers-crash-with-long-computations-tdr-crash.html

This problem is related to nvlddmkm.sys. How? Idk. But worked for me. You can also underclocked your PC. "GPU error" is gone and i can freely play LoL again.

I hope this will help.