I have seen games were you play half a year with wrong config till someone says "Hey, your break free from boss chain attack is too slow, if its still on mouse 3 then change it to keyboard" and then you see why you failed to counter boss attacks. If its just behind experience that is fine. It would be just stupid year later to find out that I have been missing most of my GB counters, because my key bind or my peripherals was limiting my reaction speed.
If you are new to the game maybe you don't know that, some specific hero moves which misses, a whiffed heavy attack, and dodges give you recovery frames. A heavy attack has attack startup vulnerability frames. Light attacks also, but only 100ms. These circumstances means you can't counter the GB.
What I think is happening for you is that you are caught by a GB in a dodge, and then you can't counter it.