Adapt and overcome.
Likely some combination of weak abdominal muscles, degenerating spine, and tight hamstrings. If your hamstrings are too tight then your sacrum is tilted back and your lumbar spine is in a tight flexed position supported by your abdominal muscles to allow you to sit upright. Adding a more supportive seat back relaxes the core muscles but forces the lumbar spine into a tighter curve. Lowering the back band shifts the pressure to the sacrum and off the lumbar spine. If you have room, raising the seat just a little can improve the angles, at the cost of reduced stability.
Finding that sweet support spot sure helped me. Recurring episodes have dropped to near zero since 1995. People were telling me to do all kinds of crazy surgery options. When I bought kayaks, I gravitated to Wilderness Systems for the seat. I find myself using the support less and may switch out to a backband. There’s a lot of untapped power in waist rotation.