Burst fire 2 is supposed to hit 3 times but it only hits 2 times. Does anyone else have this problem or is just me?
It may hit up to 3 times.
But it does not necessarily fire every time you hit. It will only go off about 1 in 3 times (give or take), and each trigger chance is successive-- if it fails to fire at any point, that instance of Burst Fire is over.
Of course if you still have anything left on your counter, and you make another attack, it has a chance to go off again.
Consider this rather typical episode with Bonnie Anne:
She attacks, and gets another attack with Burst Fire, and gets another attack with Burst Fire, and then the enemy dies. Then she gets a Double Tap, and that hits, and since she has 1 more use of Burst Fire, it goes off again.
Relentless works the same way, except with melee attacks.