@Paul_M, I certainly understand your frustration.
As I’ve expressed before: allowing System Power Manager to blindly change setInputVoltageLimit
to (3880) despite the User’s PMIC settings is detrimental to Solar Powered Borons.
I noticed that the temporary work-around included a delay (that you are missing) after the detachInterrupt from This post. Maybe that will help?
void setup() {
detachInterrupt(LOW_BAT_UC);
// Delay for up to two system power manager loop invocations
delay(2000);
// Change PMIC settings
PMIC pmic;
// your specific settings here
}