I made the assumption when I first read your post that your left impact was comparing fletched broadheads with fletched field points. But then I reread your comment about shooting with the bow in a vertical position, and wondered if you are bareshafting with broadheads? Otherwise, why would you be shooting the broadheads with the bow vertical, when you normally cant the bow? If you are bareshafting with broadheads, any unusual change in the point of impact would more likely be caused by planing than anything else.
BTW, it would be normal for arrows to impact to the left when you shoot with the bow in a vertical position if you normally shoot with the bow canted, because your dominant eye will be farther to the left of the arrow when you shoot with a vertical bow, unless you tilt your head more than you usually would to compensate for that. But this wouldn't explain why broadheads would impact to the left of field points, especially if shot with a weaker shaft. You may still be getting some planing, even with fletched shafts, and may want to try re-orienting your broadheads on the arrow shaft, so that some are vertical, some horizontal, and some in between, to see if this has any effect on the point of impact.