There was a solder bridge between GND and DEC (a NC pin), which is the output of the LDO regulator. I thought these were two GND pins and were supposed to be connected together.
So now I’m back to the same behavior as the first module: Programming failed @ address 0x00000000 (block verification error)
I have not done the other steps you prepared today on this module since the solder bridge was removed. Those will be done in the next few minutes. If that fails then I will put on a 16k module.
nrfjprog -e did it. Now there are flashing LEDs!