Hi Eljot, bold move, de-soldering and soldering on a flex pcb. What did you use? A hot air gun to get the job done or a soldering iron?
Still a strange story with the GT911. Just to be sure, you are now using the old firmware? (W25Q16 variant you downloaded from this forum)
How did you do the programming of the flash? With the device on or off? (or even with the battery disconnected?) Which programming software did you use?
Been away on family business, so not much progress on the reverse engineering yet.