I really appreciate all the ideas. I will need to really think through what might have happened.
I believe it is something in the last three days, although what that is yet hasn't come to light in my mind.
They were large eggs.....all large or extra large in size......so i can understand why the chicks had a hard time even getting a pip on the small end. Several seemed quite wet inside the membrane when opened, so makes sense they may have drowned. I do use the rails, and they seemed to stay in them well. When I put them on their sides on day 18 I always mark the lowest point of the air cell and position that on top and can normally almost predict where the pip will be. The Wellies do seem to always hatch after the hybrids.....which are a Wellie-Blue Wheaten Ameraucana cross. Those little buggers practically shoot out of the eggs and all hatch within a couple of hours of each other, then grow leaps and bounds faster than anyone else. They are a delightful cross which lays a nice light olive green egg, sometimes with speckles. I do have two lines of Wellies and these eggs were mostly from one of them......the others are a more broody line and I have a few of them sitting on eggs, so will see how those turn out.....but the line I hatched from do produce a large, chunkier chick (and bird) which makes me wonder if that brings some aspect to this.
I will follow Ruby's advice and research more about reasons for not positioning correctly. And watch my next hatch like a hawk.......maybe I was just too complacent with this one and missed something....I have gotten kinda spoiled with this incubator.
Thanks again for the input.