I’ve received your email and am answering here.
The PCBs are all manufactured by the same company since the Kickstarter campaign and are all e-tested.
We did not have any PCB-related problems or complaints so far.
Please, test the continuity on all four data lines which connect the microcontroller to the SD card.
Are all SD lines open? How many of them do not have continuity? You can easily fix this by soldering a tiny wire between two soldering pads or by scratching the red paint from the PCB and soldering a tiny wire directly to the traces.
Don’t give up!