Your milling drive needs too be re zero returned and alignment check done on the turret and milling drive. Three things I know of causes this, the slot for the live tool drive is just slightly out of alignment, so it will just grab the tool holder dog as it goes through. The other thing I've seen, although very rare , is the whole slot is offset in relation to the stationary slot around the turret. Or the turret is off center from a crash, so the holder tab is not rotating in the center of the drive. Either way, it's not for the novice to re align this, it can get challenging.