Good to hear you are seeing improvements with your shoulder position and a more neutral low back and pelvis as a result of the work you are doing.
System of systems as one area has better position(s) things up and/or downstream can improve.
The degree of impact of kyphosis and forward shoulders effect on lumbar lordosis can be impacted by cause of the condition and severity of symptoms.
The plateau with hip smashing and band distractions can happen because you made improvements available and changes in other areas were needed to continue moving toward your goals.
Improved shoulder position and improved posture have downstream effects.
Sleeping on your back more of the night is a solid improvement.