Typically, a bunch of reduction of mobility in the lumbar region that causes pain can also be caused from limitations in t-spine and hips.
Ahh, that makes sense then as something I have sort of figured out over the years in myself and gymnasts. That's why our boy's warmups would have straddle swings on rings as those do a pretty good job of loosening up the shoulders and hips which also helps loosen up the lower back.
Besides the usual t mobility drills on a roller, I found that loosening up the lower back when it's tight is extremely difficult besides the usual lay and twist. Hip mobility does seem to work. Butterfly stretch is something that I feel really tight in my lower back with.
To note our gym chiro at one gym told me and one of my star lil guys that our lower back lordosis leads to tight hips and quads.