Failed wheat harvest which caused a bread shortage.
Bread was a staple food in 18th century France.

I’m not quite sure if it is similar to the rice shortage in Japan today however. When the French couldn’t eat bread in the 18th century they went hungry, but when the Japanese today can’t buy rice they can just buy a different carb.

Its the difference between barely scraping by on bread, and being inconvenienced by not being able to buy cheap rice.