Failed to flash new ESP-12S Module, works after entering boot mode manually

[craigfoo]

I purchased a handful of ESP-12S modules directly from AI-Thinker (the manufacturing). When I first connect the module, this is the default output I get on the console as expected (hitting Enter gives me the ERROR).

Ai-Thinker Technology Co. Ltd.

ready

ERROR

ERROR

I try to flash it using the console commands:

esptool -cp COM3 -cd nodemcu -cb 115200 -cf firmware.bin -vvv

And this is the output:

esptool v0.4.11 - (c) 2014 Ch. Klippel <ck@atelier-klippel.de>
        setting port from COM1 to COM3
        setting board to nodemcu
        setting baudrate from 115200 to 115200
        espcomm_upload_file
        espcomm_upload_mem
        setting serial port timeouts to 1000 ms
opening bootloader
resetting board
trying to connect
        flush start
        setting serial port timeouts to 1 ms
                flushed 0 bytes
        setting serial port timeouts to 1000 ms
        flush complete
        espcomm_send_command: sending command header
        espcomm_send_command: sending command payload
        espcomm_send_command: receiving 2013 bytes of data
        read 0, requested 1
error: failed reading byte
warning: espcomm_send_command: cant receive slip payload data

This repeats until it fails. Then, I hold GPIO0 low and reset the chip. I run the above again and it successfully programs. At this point, I can program it over and over without having to manually enter bootloading. Not sure what's going on here. Any thoughts on this?