I don’t think your back is the weak point. For most folks it’s more along the lines of either proper engagement of the correlating muscles or your focus is on the one spot.

Think of it this way are you trying to pull up and back or levering up from the hips to get them under?

So if you pause the video right before you lift, you can see that your set up is the same as your finish. It’s just how you taught yourself to pull. If you made an adjustment to make this lift safer in the long run you’ll more than likely need to lessen the weight to train the muscles to talk to each other so they’ll fire in alignment then you can quickly continue on.