Happened when I deconstructed a bunch of entity ghosts. Did not reoccur after loading save, so I guess there is an element of timing involved.

The mod Construction Drones caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Construction_Drones::on_tick (ID 0)
invalid key to 'next'
stack traceback:
[C]: in function 'next'
Construction_Drones/script/construction_drone.lua:571: in function 'check_list'
Construction_Drones/script/construction_drone.lua:885: in function 'check_ghost_lists'
Construction_Drones/script/construction_drone.lua:1434: in function 'handler'
Construction_Drones/control.lua:37: in function <Construction_Drones/control.lua:35>