The ATB glitch is a glitch found exclusively in the Advance remake of Final Fantasy IV. The ATB gauge is new to Final Fantasy IV Advance, but the problem is the ATB system, which was always in place. It seems that some characters get extra turns when the battle speed is set high. For instance, a character's ATB bar will be 1/3 full, and then all of a sudden the player gets another action with them. The issue seems to be the constant input of commands.
This makes certain skills like Kain's Jump and Yang's Power appear as if they are delayed. The player could choose Jump for Kain and any number of other actions for the others and he may not jump for two or three turns. However, what is more likely the case is that Kain's Jump is executed in normal speed, only he is unable to benefit from the extra turns the other characters get.
This glitch also means enemies often act sluggish or their turns are skipped completely, so the game will seem easier than it used to be for at least the first half of the core game.