Current.log: https://pastebin.com/atgc4XZj

Error while running event Construction_Drones::on_ai_command_completed (ID 113)
Construction_Drones/script/construction_drone.lua:1634: attempt to concatenate field 'unit_number' (a nil value)
stack traceback:
Construction_Drones/script/construction_drone.lua:1634: in function 'move_to_order_target'
Construction_Drones/script/construction_drone.lua:1997: in function <Construction_Drones/script/construction_drone.lua:1984>
(...tail calls...)
Construction_Drones/control.lua:37: in function <Construction_Drones/control.lua:35>

commenting out line 1634 seemed to fix it. It appears a debug message that assumes the target will have an entity id. I seemed to reproduce this by marking trees for deconstruction and then walking away until my I am too far from the deconstruct zone for the drones to continue.