ERROR:
The mod WH40k: Titans (1.0.4) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event WH40k-Titans::on_tick (ID 0)
WH40k-Titans/script/assemble.lua:817: attempt to index field '?' (a nil value)
stack traceback:
WH40k-Titans/script/assemble.lua:817: in function '?'
WH40k-Titans/script/assemble.lua:914: in function 'process_an_assembler'
WH40k-Titans/script/assemble.lua:965: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

Info:
Crashes server when moving Titan or Supplier over Assembly Bunker when Assembly Bunker is in ammo restocking mode. This is running on our dedicated server but I have copied the save and issue persists in single player as well. We have several other mods running (listed below),but even when I disable all other mods issue persists. Tried with both base game and also Space Age with same result. Also tried picking up the bunker and setting back down, issue persists.

Factorio Version: 2.0.21
WH40k Version: 1.0.4

mod-list.json:

{
"mods":
[

{
  "name": "base",
  "enabled": true
},

{
  "name": "elevated-rails",
  "enabled": true
},

{
  "name": "quality",
  "enabled": true
},

{
  "name": "space-age",
  "enabled": true
},

{
  "name": "Aircraft-space-age",
  "enabled": true
},

{
  "name": "combat-mechanics-overhaul",
  "enabled": true
},

{
  "name": "Common-Industries",
  "enabled": true
},

{
  "name": "Flare_Stack_SA",
  "enabled": true
},

{
  "name": "HelicopterRevival",
  "enabled": true
},

{
  "name": "informatron",
  "enabled": true
},

{
  "name": "invincible-construction-bots",
  "enabled": true
},

{
  "name": "jetpack",
  "enabled": true
},

{
  "name": "lex-aircraft",
  "enabled": true
},

{
  "name": "mining-patch-planner",
  "enabled": true
},

{
  "name": "Nanobots2",
  "enabled": true
},

{
  "name": "Repair_Turret",
  "enabled": true
},

{
  "name": "Reverse-Engineering",
  "enabled": true
},

{
  "name": "some-corpsemarker",
  "enabled": true
},

{
  "name": "SpidertronEnhancements",
  "enabled": true
},

{
  "name": "SpidertronPatrols",
  "enabled": true
},

{
  "name": "stdlib2",
  "enabled": true
},

{
  "name": "StorageTank2_2_0",
  "enabled": true
},

{
  "name": "Swedish-Chefbots",
  "enabled": true
},

{
  "name": "vehicle-corpses",
  "enabled": true
},

{
  "name": "Vehicle-Teleportator",
  "enabled": true
},

{
  "name": "WH40k-Titans",
  "enabled": true
},

{
  "name": "WH40k-Titans-media",
  "enabled": true
}

]
}

Hi! Thanks for reporting, and sorry for bad experience :( Recently I've also observed this issue, and plan to publish a fix today or tomorrow.

Thanks for the fast response! Happy coding!

I've published new v1.0.5, have a try!
Btw, the problematic code was only about restocking Aircraft Suppliers (code line mentioned in your error message also was related to aircrafts specifically), and restocking of Titans worked well for me. In case you really meet an error with Titans, it shall be a different error – let me know.

Thankyou for fixing this issue with the Aircraft Suppliers in v1.0.5! We have tested it and confirmed it did resolve the issue with the Aircraft Suppliers.
The issue still persists with the WarLord Titan (we have not tested all Titans). I missed that it was a different error message that was given with the Aircraft Suppliers and WarLord Titan. Below is error given when the Warlord attempts to restock at the Bunker:

The mod WH40k: Titans (1.0.5) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event WH40k-Titans::on_tick (ID 0)
WH40k-Titans/script/assemble.lua:795: attempt to perform arithmetic on field 'inventory' (a nil value)
stack traceback:
WH40k-Titans/script/assemble.lua:795: in function '?'
WH40k-Titans/script/assemble.lua:914: in function 'process_an_assembler'
WH40k-Titans/script/assemble.lua:965: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>