It looks like a commit last week to the 15.1 branch broke builds for hammerhead:
ERROR: /mnt/second/android/lineage15/packages/apps/LineageParts/src/org/lineageos/lineageparts/livedisplay/LiveDisplaySettings.java:401.60: config_enableLiveDisplay cannot be resolved or is not a field
I’m seeing discussion about this on other devices (https://www.reddit.com/r/LineageOS/comments/feuc3e/build_for_mako_fails, for example) that indicates that this isn’t isolated to hammerhead. It seems that devices that don’t have active maintainers weren’t updated to handle a feature change.
15.1 on hammerhead builds are going to fail until this is fixed.