Oh man, that's such an easy mistake. I mean, a few degrees feels like nothing until you see the chain just dusting the wood instead of biting in. I kept getting these wavy cuts on some logs last fall and it drove me nuts. Finally checked the angle with the little guide and sure enough, I was off. It makes a huge difference once you fix it.
You were getting wavy cuts last fall and only just now figured it out? That's wild, I would have lost my mind. My neighbor had the same thing happen and his logs looked like a roller coaster track. Those few degrees really do trick you until the saw just stops working right.