This has happened to me as well. Mostly over the last month or so. I haven't really kept track of which mons I was trying to catch when it happens. Maybe they have some telekinetic defensive ability... Or maybe I'm just not being careful about finger location on the screen and messing up my curveball motion, i.e. while spinning the ball, move too low on the screen at the toss and lose the spin?
Curveballs not curving reliably?
Anyone else had an issue where their curveballs just... stop curving? You get the flashing animation like normal but when you throw it, it goes straight off the screen or beside the Pokémon and never curves.
Seems to be happening more to me since Groudon was released, where I'll do my normal curveball action, but about every 3rd or 4th ball (hard to tell exactly how often it happens) the ball just simply doesn't curve. (Amusingly I just caught a Roselia with a curveball that went off the screen, and for the first two beats of the Pokeball, there was nothing on the screen.)
I used to think I just did it wrong, but for months now every time I've done a curve, the ball did actually curve. (sometimes more than I wanted. Much more. grr.) Now I'm not so sure.
Answers
Yes, 3-4 times in the past week. I had wondered whether it was "operator error," but it's happening more frequently lately. Sure, occaisonally I make a bad throw (and know when I release a ball that I did); but I've caught nearly 24k pokemon and tossing pokeballs mostly comes from "muscle memory" now. One recent errant curve was definitely due to lag, though.