1. i never said to crack the back, (only gently stretch)
2. I didnt say it would fix the problem i said if it relieves pain, (as i also followed up with how to strengthen)
If pain is relieved when performing a backwards bend/stretch it is recommended to perform them slowly and controlled imediatly after recieving the pain, and throughout the day/workout session to...
Possibly even a weak lower back. If your lower back muscles arnt all that strong then thats what would be causeing the hyperextension of the lower vertibre.
Keep doing what your doing, just perhaps raise the weight so that you fail at about 10.
Just keep an eye on those elbows though, because you are hanging at the bottom of your reps (Plus the added...