The mod Laser Lines caused a non-recoverable error.
Please report this error to the mod author.

Error while running event laserlines::on_built_entity (ID 6)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
laserlines/control.lua:102: in function 'target_id'
laserlines/control.lua:110: in function 'target_state'
laserlines/control.lua:189: in function 'emitter_beam'
laserlines/control.lua:322: in function 'emitters_update'
laserlines/control.lua:354: in function <laserlines/control.lua:327>
stack traceback:
[C]: in function 'index'
__laserlines/control.lua:102: in function 'target_id'
laserlines/control.lua:110: in function 'target_state'
laserlines/control.lua:189: in function 'emitter_beam'
laserlines/control.lua:322: in function 'emitters_update'
laserlines/control.lua:354: in function <laserlines/control.lua:327>

Thanks. This should now be fixed in 0.1.4.

Although it should no longer crash, removal of cliffs may still require manually rotating the laser to force an update because the on_entity_died event apparently doesn't arrive for cliffs, and the only events specific to cliff removal are for robot actions, not player actions. Must be missing something...