BPI-M2 Zero: Power over GPIO not working, stuck at boot

Trying to power up the BPI ove GPIO but it’s not working for me. Using GPIO pin 4 and 6. It gets stuck at the boot screen, usually here:

U-Boot SPL 2017.09-h2 (Jul 06 2018 - 10:16:12)
DRAM: #  

The same PSU connected over USB boots fine. Tried a few different PSUs, same results.

Any suggestions?