The mod Factorissimo2 Playthrough (1.2.1) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Factorissimo2-Playthrough::on_research_finished (ID 18)
Factorissimo2-Playthrough/scripts/gui.lua:311: attempt to index field '?' (a nil value)
stack traceback:
Factorissimo2-Playthrough/scripts/gui.lua:311: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

What mods do you have enabled? This seems weird.

Maybe it's incompatible with this mod?
https://mods.factorio.com/mod/UltimateBelts_Owoshima_And_Pankeko-Mod