It looks like having Injustice on my phone causes my phone to become VERY unstable. Apps start misbehaving and being terminated by the Android OS as it attempts to free-up memory, even when Injustice is not running. I’ve had to remove it off my phone just to get it to behave properly, so now I’m playing it on my tablet instead. I lost around 1 day’s worth of play, but that’s tolerable since I’ve just started it.
Progress is slow, since I can only use the app when I’m at home. But still, I’ve managed to gain some more levels and characters. I’ve even promoted Nightwing and Catwoman.