Keep assessing globally and aim to find the key link.
That said, some of the patterns that have worked require more optimal core integrity….essentially normalizing the core. Not muscle specific but an adequate and appropriate balance of activity based on the load or demand placed on the system. Proximal stability (maintenance of expiratory position and cylindrical core activation) in the presence of distal mobility (extension movement of the hip)
Kneeling ball rollout
Push up variations
Once saggital stabilization is established, rotation moments are then assessed and challenged.
Make sure the T-L junction has good motion and that there is no, and I mean zero malposition of the pelvis. Rule out any tight hamstring issues or anterior pelvic tilt from tight quads, which either way leads to chronic shortness of the iliopsoas. Iliopsoas has a huge number of attachments in the trunk to flex the hip without falling over, but when short, in standing, it pulls the lumbar and last thoracic vertebrae forward and down. Look at the whole ribcage – take your finger and palpate between every rib and find active intercostal trigger points. No one hardly ever does this for clients…a lot is missing in between those ribs related to Tsp.
You get my point – keep looking globally, work locally at the T-L junction, the intercostals, more psoas. Maybe the hamstrings and quads. Make sure the person learns what a stable pelvis feels like and facilitate/strengthen muscles to keep it there.