I have same kind of symptoms when updating firmware with my htc one m7.

Fw-update seems to go as planned, but after reboot it says “Bootloader, Invalid firmware” and blinks steady 1 sec on, 1 sec off. This happens on every app-version after ~1.0.11 (not 100% sure, last tried to install everything i found few weeks ago)

But, everything works again, if i downgrade to 1.0.10 app and install fw 1426035947. Then i can update app to 1.0.16 and it works, as long as i would not let it touch the firmware.

I have also tried different batteries, with and without sd-card, tried that “wakeup routine” and so on. I’ll have to hijack another phone from some friend to see if that helps..