@howil and others - this needs a hardware rework, change one capacitor. The ODM was very helpful in troubleshooting this, but we cannot address it in firmware since the tuning improvements above were not sufficient.
Please contact support@puri.sm if you would like to discuss an RMA or out-of-warranty repair. If you are comfortable replacing an SMT capacitor, you can make the change below.
This capacitor on the bottom of the board needs to be replaced with 22 uF 6.3V 0603 on affected devices.
My apologies for taking so long to reach this solution. I was very hopeful for a firmware fix since the changes each showed measurable improvements on devices I have, but there’s no farther we can go in firmware. This change fixed the issue on both affected devices that I have with the current firmware release, no tuning changes were needed.