I would not necessarily expect 100% "insta-kill" from body shots. Even though I have personally witnessed it nearly 100% of the time, myself, on woodchucks.
I have shot 3 woodchucks with 12ga deer slugs. Would you believe that every one of them escaped? It's hard for me to believe and I saw it with my own eyes. Trails of all manner of nastiness leading back to their holes but all 3 made it.
What am I to make of it? Bullet failure? 12ga isn't "enough" for woodchucks?
Sheer dumb luck and poor shot placement, intermingled unpredictably. That's what caused it.
Squirrels? Are you talking, like, Grey Squirrels?! There's no way a 17HMR doesn't kill squirrels with any kind of shot placement. The 17 will blow squirrels in half.
Crows? I've seen at least 3 killed with a 17. 3 is not a normal statistical sample but the effect has been so devastating that I find the idea of wounding them, again, with any kind of shot placement, to be pretty far fetched. For all intents and purposes, it blows them in half.
I/We have used Hornady and CCI ammo with indistinguishable results. When we make the shot, the 17 has never failed us, not once.