Fix for fastboot problem
The last two nightlies have had issues with the kernel and should not be installed directly as you will be stuck on fastboot mode.
The last known good nightly is 20171009, the problematic ones at the time of this writing are 20171023 and 20171030.
However, the broken builds can be installed if you manually take care of the kernel (BOOT) and work properly with the 20171009 BOOT.
The following guides expect you to have a working fastboot/adb stack on your computer and to be comfortable with copying files and keeping track of paths. There are many guides around to help you with fastboot.
If you want to update past 20171009 from a running LineageOS follow these steps:
1) Download the current nightly on the phone (know where your files are!)
2) Reboot into TWRP
3) Backup the BOOT partition (the rest is not required, but it's always a good idea to have a full backup anyway)
4) Install the current nighly build, wipe cache/dalvik
5) [Optional] Install gapps, su, xposed, modem, etc.
6) DO NOT REBOOT TO SYSTEM YET! Restore the BOOT partition from the backup you just created
7) Now reboot to System, it should work
If you updated automatically (or manually without taking care of BOOT) and got stuck into fastboot, do this:
1) Download the TWRP linked in the first post, remember the path to this downloaded file on your PC
2) Download both the 20171009 and latest builds of LineageOS
3A) Copy the LineageOS builds you downloaded to a microSD card (must not be formated as internal) and install it into the phone
3B) Copy the LineageOS builds you downloaded to an usb thumbdrive if you have a microusb-to-usb cable
4) Connect the phone (turned on and on fastboot mode) to a the with a running fastboot/adb stack
5) Run this command (from CMD with administrative rights on Windows, Shell on Linux or Mac): fastboot boot [path to the downloaded TWRP]. After a few seconds TWRP should start on the device.
6) [Only if you DON'T have a backup of BOOT from 20171009] Install the build from 20171009 either from the microSD card or (after connecting the microusb-usb adapter and thumbdrive to the phone) USB drive, then wipe Cache/Dalvik
7) [Only if you DON'T have a backup of BOOT from 20171009] Backup at least the BOOT partition
8) Install the latest build you downloaded (20171030 at the time I wrote this)
9) [Optional] Install gapps, su, xposed, modem, etc.
10) DO NOT REBOOT TO SYSTEM YET! Restore the BOOT partition from your backup
11) Now reboot to System, it should work
Both methods were tested and confirmed working by myself on a G620S but should work on any device that this rom supports.
