It's making me crazy as well. We just had our 4th replacement of an iPhone6 64gb gold. Everytime the same issue. Now it's at the left and right bottom corner, but previously is was at different positions on the screen.
First replacement took place 2 weeks after we bought it new from the Apple store.
2nd Replacement was the replacement service for 29 euro. Both 3rd and 4th replacements were for free. Indeed, Apple support from now on sells it 'as being normal', but I'ld like to know how we should deal with that. I'm not going to repair the phone myself...