Hi !
I successfully made a fresh install of Sailfish OS 2.1.3.7 !
In a nutshell, the instructions could be summarized in 3 steps:
- fastboot flash modem NON-HLOS.bin from FP2-gms59-1.5.1-manual.zip
- fastboot flash system system.img from fp2-sibon-18.02.0-manual-userdebug.zip
- TWRP > install sailfishos-fp2-sibon-release-2.1.3.7-alpha5.zip
@mal I didn’t flash the recovery.img, as I already have the last TWRP 3.2.1 installed 
For my previous corrupted image, reflashing the system.img from 16.10 didn’t help. But anyway I managed to get my files back with adb pull /data/.stowaways/sailfishos/home/ 