Could be a number of factors. Is this an Arsenal SLR-104UR? If so, I purchased two of them and both had canted rear sights. You cant fix the rear sight without drilling out the rivets, repositioning the sight, drilling and riveting it back together. This was something I didn't want to do to a brand new rifle, so I returned them.
I just built a Bulgarian AKSU from a demilled parts kit and the FSB/GB is canted to the left. So once again, the front sight post has to be pushed pretty far to the right in order to zero. I could tap out the pins, press off the FSB/GB, reposition, and repin but I'm just going to leave it alone.
I am super OCD and it took me a long time to accept that as long as the rifle can be zeroed not to worry about how centered the front sight post is. I've seen tons of Bulgarian kits with canted parts, so it's part of their nature.
Turn the rifle upside down and see if the rifle rests at an angle. If it does, see what part is causing it to position that way. From my experience, it is normally the rear sight.