Usually when you aim in with any scope, the point that the scope aims into (and sometimes binoculars?) is supposed to be the same point that you were looking at as you were aiming in (if I point the cursor aka white dot in the middle of the screen at something, I should then be looking at that same point with my scope once I'm ADS.) I've noticed consistently when aiming down sight with any scope (or at least all the ones I've ever used) while speicifically in the prone position on any kind of hill or slope, that the point which you were originally aiming at drastically changes downwards... I'll explain more in the steps to reproduce.
I'm marking this as a major severity because it can easily change the outcome of a gunfight, a part of the game that should probably be more mechanically flawless than anything else.