It seems to be a bit of a bug with part of the experience bonus during the current Fire and Ice event.
Part of the bonus was added to your accurate throws and the first throw bonuses. People don’t have much problems catching Pokémon on their first throw but since the event started, trainers have noticed a decrease in catching Pokémon with their first PokéBall.
This could be a bug or perhaps it’s just because they are focused more on filling the missing PokéDex.
Pokemon of all types seem to be popping out of PokéBalls left and right. Rather it’s a great or ultra ball. It is possibly that Niantic lowered the catch rate of Pokémon during this event to prevent trainers for leveling up too fast. Though, it’s more than likely only a bug from servers being overloaded.