LineageOS 14.1 update: stuck in TWRP recovery

https://www.reddit.com/r/LineageOS/comments/5rarac/tried_updating_nightly_stuck_in_twrp_recovery/

• reboot to bootloader, then run "fastboot continue" on PC. phone continues to boot normally. BUT: A normal reboot goes straight into TWRP recovery again (TWRP 3.0.0.0)

official twrp crackling support thread: - - https://forum.xda-developers.com/wileyfox-swift/development/recovery-unofficial-twrp-3-0-1-0-t3350351/page5#edit70641502

• "need to update, flash this"
  • fastboot-20170119-crackling.zip from https://androidfilehost.com/?fid=529152257862696687
• "You probably have to flash a new version of fastboot first. Look at post #46 in this thread."

Flash new fastboot by unzipping fastboot-20170119-crackling.zip and then:

$ sudo fastboot flash aboot emmc_appsboot.mbn
target reported max download size of 268435456 bytes
sending 'aboot' (534 KB)...
OKAY [  0.019s]
writing 'aboot'...
OKAY [  0.011s]
finished. total time: 0.030s

Now I can reboot to TWRP 3.1.1-0