LineageOS 14.1 installed, TWRP 3.0.0 installed, phone working properly. After an OTA update gone wrong, the phone did not boot into system but only into TWRP recovery.
Based on https://www.reddit.com/r/LineageOS/comments/5riech/how_fix_twrp_recovery_boot_loop_after_lineageos/ the first try was to install a newer version of TWRP. This resulted in the phone unable to boot at all.
fastboot erase recovery fastboot flash recovery twrp-3.0.0-0-crackling.img
TWRP 3.0.0 available again
Flash most current version of LineageOS –> no change
https://www.reddit.com/r/LineageOS/comments/5riech/how_fix_twrp_recovery_boot_loop_after_lineageos/
fastboot continue
adb shell dd if=/dev/zero of=/dev/block/platform/soc.0/7824900.sdhci/by-name/misc bs=32 count=1