I did try flashing to recovery and then restart to recovey, but that just dumps me back into fastboot. Most likely due to the same issue.
I know my way around python and some C/C++, but I have never done anything for Android.Looking back through the thread, I can't see anyone reporting this twrp working for the X605FC. Only reports of problems. So I guess I'll have to call it: the official twrp for the X605F won't work on the X605FC. I'll update the OP.
Building twrp for X605FC
If you're a developer, it's a trivial matter to modify the DT for the X605F.
I wouldn't know where to start. The build description of TWRP is rather sparse and seems to assume a lot of android knowledge.