got the following error message:
Error MainLoop.cpp:1435: Exception at tick 81587552: The mod What is really missing? (3.0.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Kux-WhatIsMissing::on_tick (ID 0)
LuaRecipePrototype API call when LuaRecipePrototype was invalid.
stack traceback:
[C]: in function 'index'
__Kux-WhatIsMissing/modules/EntityScanner.lua:88: in function 'checkMachine'
Kux-WhatIsMissing/modules/EntityScanner.lua:169: in function 'on_execute'
Kux-CoreLib/lib/AsyncTask~prototype.lua:109: in function 'execute'
Kux-CoreLib/lib/AsyncTask~prototype.lua:53: in function 'on_tick'
Kux-CoreLib/lib/AsyncTask.lua:209: in function 'fnc'
Kux-CoreLib/lib/EventDistributor.lua:156: in function <Kux-CoreLib/lib/EventDistributor.lua:150>

did you remove or change machines? the prototype becomes invalid for a reason.
I can catch the crash and ignore the machine but This could lead to calculation errors that are not visible.
Can you provide a savegame with this error?

happy new year