The crash happend when my bots built a tib spike. Looking into the code of both mods, it seems like the 'tibGrowthNode_infinite' entity created by this mod somehow ends invalid when Big Monsters tries to look at it's surface. Is it supposed to disappear that fast?

I have no idea what Big Monsters is doing.

it's doing this

function On_Built(event)
local entity = event.created_entity
local surface = entity.surface

The last line is where it crashed

Ya know, the error message you actually got would be very helpful.

6835.991 Error MainLoop.cpp:1207: Exception at tick 12684956: The mod Factorio and Conquer: Tiberian Dawn (1.0.5) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Factorio-Tiberium::on_robot_built_entity (ID 14)
The mod Big-Monsters (1.0.1) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Big-Monsters::script_raised_built (ID 77)
Big-Monsters/control.lua:777: attempt to index local 'entity' (a nil value)
stack traceback:
Big-Monsters/control.lua:777: in function <Big-Monsters/control.lua:775>
stack traceback:
Factorio-Tiberium/control.lua:805: in function <Factorio-Tiberium/control.lua:761>
stack traceback:
[C]: in function 'create_entity'
Factorio-Tiberium/control.lua:805: in function <Factorio-Tiberium/control.lua:761>

Modifying Big Monsters with escape patters for invalid event entities seemed to have prevented it from repeating, so my guess is that an entity gets created and instantly removed or something, which causes Big monsers to attempt to referance a non existant entity.

So they're not properly checking entities before they try to do something with it.

I do wonder what entity of our triggered that though...

Pretty sure it was the one that spawns when I placed the tib spike. The resource one.

Yeah, but I'm not sure how that one could possibly have done that. It stays there.

Big-Monsters ran into the issue that I was complaining to James about a couple of months ago: different events have differently titled subscripts, even though you want to use them with the same function. When our node swapped to infinite, it fired a raise_built but Big-Monsters didn't use the correct subscript in that case (entity instead of created_entity) so they got a nil.

https://mods.factorio.com/mod/Big-Monsters/discussion/5f4f8120d1f68850e6478362