This happened when I pushed an ingredient in a recipe. This was the second time I had done this, the first time it replaced the current recipe with the ingredient and the second time it crashed.

Error while running event RecExplo::on_gui_click (ID 1)
RecExplo/lua/explo_gui.lua:237: attempt to index field '?' (a nil value)
stack traceback:
RecExplo/lua/explo_gui.lua:237: in function 'draw_history_item'
RecExplo/lua/explo_gui.lua:176: in function 'draw_history'
RecExplo/lua/explo_gui.lua:266: in function 'update_local_history'
RecExplo/lua/explo_gui.lua:70: in function 'update'
RecExplo/lua/events.lua:330: in function <RecExplo/lua/events.lua:26>