If you have a modded game and add a modded signal to the GUI and then remove the mod, that contains this signal, the game crashes when you open the GUI. I think thats a simple fix, that can prevent alot of hassle, especially if you are already trying to find the buggy mod or reduce the save file to a minimum working example, in my case.

The mod LTN Combinator Modernized (1.0.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event LTN_Combinator_Modernized::on_gui_opened (ID 85)
Unknown sprite "item/se-scrap"
stack traceback:
[C]: in function 'newindex'
__LTN_Combinator_Modernized/script/gui.lua:58: in function 'update_net_id_buttons'
LTN_Combinator_Modernized/script/gui.lua:171: in function 'Open'
LTN_Combinator_Modernized/script/gui.lua:704: in function <LTN_Combinator_Modernized/script/gui.lua:700>

Ok, It is not because of a removed signal in the GUI, but a removed signal I used for a Network ID. The former actually works fine. The error report makes alot more sense in this case, because it actually was the se-scrap item signal, that I used.

https://github.com/kryojenik/LTN_Combinator_Modernized/issues/5