This error occurred not long after completing Mining drone speed 9 research with Krastorio 2 mod
I think I might have tried going beyond the research limit

Error while running event Mining_Drones::on_tick (ID 0)
LuaEntity API call when LuaEntity was invalid
Stack traceback:
(C): in function "index"
__Mining_Drones/script/mining_depot.lua:1089: in function 'request_path'
Mining_Drones/script/mining_depot.lua:1028: in function 'process_request_queue'
Mining_Drones/script/mining_depot.lua:1052: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

This also about an hour or two before 1.1.15 Factorio update

I haven't noticed till now, but I'm two updates behind which should have resolved my error

its not solved yet i just got the same error :

De modificatie Mining Drones (1.1.6) heeft een niet-herstelbare fout veroorzaakt.
Rapporteer deze a.u.b. bij de auteur van de modificatie.

Error while running event Mining_Drones::on_tick (ID 0)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
__Mining_Drones/script/mining_depot.lua:1094: in function 'request_path'
Mining_Drones/script/mining_depot.lua:1033: in function 'process_request_queue'
Mining_Drones/script/mining_depot.lua:1057: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

i do really like your mod tho its such a nice way to mine