It depends on how many people you followed/unfollowed in a 1 hour period. Sometimes it's a glitch other times it's the app and other other times It could be your getting hacked or spammed. Mostly I'd think if you're following/unfollowing so many people in a 1 hour period then that's why. Usually it's maybe because you're receiving something and again the 1 hour period thing. I really don't know why but I've had the same problem and it's usually when I'm about to get a game notification or a facetime call or I've followed/unfollowed to many people in a 1 hour period. This doesn't really help sorry!