I purchased several of these boards (from your Aliexpress shop) and I have had a few I cannot program.
Basically, when I plug the units in that I cannot program, I see the Red Power led but NO BLUE Led (the successful ones I could program, when first plugged in had the Red power LED on and the blue led was faintly on). The PC registers the unit and can see a valid Com Port but that is all. Trying to program them (with various different software and cables) just shows the usual timeout error. I have jumpered GIO0 and Ground, still does not work. I have noticed with the ones that I have programmed, I had to press BOOT at the time of programming. I have also tried that with the ones that are failing, and they still dont work.
Do you have any ideas on how I can test these boards to see what the problem is?
It seems they might have not been programmed with any bootloader, or base firmware.