I wasn't meaning to address that specifically to your situation, just the general concept that lost game automatically implies a lazy hunter or a shot that shouldn't be taken. Your situation sounds pretty cut and dry but I've seen an awful lot that were unexplainable.
One time, I was sitting in a large pine tree using a Rem 870 12ga with Winchester Super-X 2-3/4 slugs. I had a small-ish buck and a large doe walk directly under the tree. I took the shot on the buck, straight down, aiming for the heart, having made similar shots several times before. He dropped like a stone and the doe ran about 30 yards up hill and stopped broadside. I put the crosshairs on the center of her vitals and fired. She blaated, took a few stumbling steps sideways and tipped over in the brush, out of sight.
I looked down and the buck was gone. I climbed down and looked around for a minute or two but found no sign at all so I figured I'd go get the doe and look for him when my father came down the hill.
I went up to where the doe was and she was GONE. I managed to find a few drops of blood and followed her trail about 100 yards, my dad was there by then and neither of us could find any more sign. We circled through every inch of woods we could access, which was a good 300 yards in every direction and never found another sign.
Back to the buck, we looked for a solid hour and never found a SINGLE drop of blood or any indication of which direction he might have even gone. We circled around in that general area too, as he had been facing the opposite direction of the doe when I shot, but never found a thing.
I have never managed any reasonable explanation for those two deer. I shot the gun back at camp and it was fine. I killed a couple more deer that year too, much "harder" shots and had no trouble. Those two, I'll never know.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.