I battle this all the time, I don't believe that it is the "gold corner" that is causing the problem but something with the PCB layer makeup (copper planes, or bottom side components, etc.). It could also be the nozzle you are using has a "hot spot/coldspot". To verify I would put the BGA on 180 Deg. out of rotation and try it again and see if it follows the corner of the part or the location of PCB.
Let us know what you find.
Russ
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