fastboot boot with a signed TWRP image fails with the error:
downloading 'boot.img'...
OKAY [ 0.344s]
booting...
FAILED (status read failed (Too many links))
finished. total time: 0.359s
Edit: Ok, some minutes later I have tried again and there are no errors. The phone ends up in a boot loop though… 
I’m trying to get a photo that I took with this FP2, but I sold the battery to friends, who needed a new one… 