If you look at the specifications sheet, the Strix GTX 1080 OC model has an official GPU boost of 1936 MHz. So stability is guaranteed up until that point. Any extra megahertz that you manage to squeeze out of the graphics card is considered overclocking. Your sample doesn't seem to be stable at 2050MHz at higher resolutions. What you can do is downclock the GPU Clock to maybe around 2000MHz - 2025MHz to find your stable frequency.
That doesn't really make sense though does it. Why would the card advertise having an oc mode that it cannot run.
What is the limiting factor here?
If you haven't already you could try increasing the voltage to 100%.
On my ROG Strix 1070 it only adds another .03v which is hardly anything, I'm not sure what the max voltage for the ROG Strix 1080 is but it barely affects temps and might let you hit 2100MHz+.
If you try it let us know how it goes. 🙂