Just like how the body can only digest so much food, there's also a point of diminishing returns with training. Your body can only handle so much. If you're following a hard training protocol and going balls out, you need to sacrifice some sets and volume for a strong body part and apply that energy to a weaker one.
Let me repeat: Do not just add volume on top of volume if you're already training balls-out hard.
Here's a real world example. I worked with top national level competitor Brad Davis and he saw great improvement in his legs, which had been his weakness. Our strategy was to scale down his back training – his back was already world class – from once a week to once every two weeks, and train his legs three times over two weeks. The result? He didn't lose an ounce of muscle from his back and his legs improved dramatically.
Here's how we attacked it:
Then we'd start back at week one.
Here's a variation I had Shelby Starnes doing. His weakness was arms lagging behind his torso.
You can continuously repeat these rotations until you've fixed the problem. Remember, these are weak body parts for a reason, and they won't change overnight. It will be a fight, but you have to put your mind to it and grind relentlessly.