Just walking around when this occurs, is there a hard limit on drones or something?

The mod Long Range Reusable Delivery Drones (2.0.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Long_Range_Delivery_Drones_Durable::on_tick (ID 0)
...ry_Drones_Durable__/script/long-range-delivery-drone.lua:593: attempt to perform arithmetic on a table value
stack traceback:
...ry_Drones_Durable__/script/long-range-delivery-drone.lua:593: in function 'update_logistic_filters'
...ry_Drones_Durable__/script/long-range-delivery-drone.lua:631: in function 'delivery_requested'
...ry_Drones_Durable__/script/long-range-delivery-drone.lua:1014: in function 'try_to_schedule_delivery'
...ry_Drones_Durable__/script/long-range-delivery-drone.lua:1210: in function 'update'
...ry_Drones_Durable__/script/long-range-delivery-drone.lua:1259: in function 'update_request_depots'
...ry_Drones_Durable__/script/long-range-delivery-drone.lua:1337: in function 'handler'
core/lualib/event_handler.lua:72: in function <core/lualib/event_handler.lua:70>

It seems completely random.

The mod Long Range Reusable Delivery Drones (2.0.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Long_Range_Delivery_Drones_Durable::on_tick (ID 0)
...ry_Drones_Durable__/script/long-range-delivery-drone.lua:349: bad argument #1 of 2 to 'next' (table expected, got nil)
stack traceback:
[C]: in function 'next'
...ry_Drones_Durable__/script/long-range-delivery-drone.lua:349: in function 'deliver_to_target'
...ry_Drones_Durable__/script/long-range-delivery-drone.lua:533: in function 'update'
...ry_Drones_Durable__/script/long-range-delivery-drone.lua:1295: in function 'update_drones'
...ry_Drones_Durable__/script/long-range-delivery-drone.lua:1339: in function 'handler'
core/lualib/event_handler.lua:72: in function <core/lualib/event_handler.lua:70>