We should have response a lot earlier, sorry again.
Root cause: The latest batch (During Oct) of Seeeduino shipped might have wrong fuse, which will cause bootloader sector get skipped. For the first time we upload test program via bootloader, it is all right. But if the device is repowered, the MCU does not go into bootloader anymore.
1) Please refer to the quick fix by Bitbang mode as the last post from Albert
if it is too much trouble,
2) we are more than relieved to replace one for you.
We did serious testing to the Seeeduino shipped, [visual inspect -> program bootloader -> functional test of each pin -> package]. But we still need a complete process to cover the exceptions. The damage to our quality and your time is permanent. Please let us know if any assist needed. Sorry for the huge inconvenience brought!
Thanks for your support!