Fairphone Open 17.02.0 is now available

For updates of an installed OS, Fairphone recommends the use of the Updater App anyway (at least on the download page for Fairphone OS with Google services).

Update files for use with TWRP have “ota” instead of “manual” in their filenames, see download links at Fairphone Open OS downloads “OTA” or at Fairphone OS downloads anywhere but not “4. Flash the binary images from a computer”.

fp2-sibon-17.02.0-manual-userdebug.zip is not for use with TWRP, it is used with fastboot on your PC with the phone connected via USB in fastboot mode, see this guide, and it is not an update, it is a new install of your phone, erasing all your data.

I don’t have enough knowledge of TWRP and the OTA update process to say whether “unable to mount” errors would make a successful update via TWRP impossible, if you use the correct OS file, but you can get around “unable to mount” errors by wiping the partition that gives the error (TWRP - Wipe - Advanced Wipe - only check the partition that gives the error) … Of course, always be extra careful with wipe, I would always try the Updater App first.