Just FYI, We did measure sleep current on RAK4631 running on a Wisblock base board using a nordic PPK2. We measured an average of 24uA.
From what i can see, the RAK4631 has VBAT_NRF wired to a higher voltage than the 3.3V when plugged into the wisblock base board. I tried to emulate this config on my hardware by connecting just the VBAT_NRF to 3.6V while all other VCC pins (VBAT_SX, VBAT_IO_SX and VDD_NRF) are connected to 3.3V. The RAK4630 module didnt come up and looked like it was resetting during power up (like a brownout reset)