Thanks for that.
The key line in that application, that imposes the sleep, appears to be;
NRF_POWER->SYSTEMOFF = 1;
On my NRF52840 plus that yields a sleep current of 1.75mA. A NRF52840 ProMico board with the same code has a sleep current of 0.19mA.
Can the sleep current be reduced further ?
I note that for the NRF52840 SEEED advertise a ‘Standby power consumption: <5μA’ which is a long way from 1.75mA.