A recent study using digital fluoroscopic video (DFV) may have some answers to your question. DFV is a type of X-ray that allows us to see the spine move. Rate, speed, and angle of motion can be captured on video and measured.
DFV images can be taken in normal adults without low back pain and compared to the same movement pattern in patients with low back pain. By finding out exactly what’s going wrong, treatment can be directed to restore normal motion.
The catching or slipping you describe has been seen in DVRs of patients with abnormal neuromuscular control. This means the muscles aren’t contracting when and how they should. Movement occurs at the wrong time, such as too late in the flexion-extension cycle.
The ligaments have to hold on to prevent too much motion at the wrong time. The disruption in the normal timing and amount of motion may be what’s causing the catching sensation. You should consult with an orthopedic surgeon to be certain there isn’t something else going on in your situation.