Smokescreen.
Sometime in the early 1340s, there was a massive volcanic eruption. No written record of the event is known to survive, the exact date and location are unknown. Technically, we are not even sure if it was a single eruption, or multiple ones. We do know it happened, and that it was likely somewhere near the equator. What evidence we have for this event is in physical evidence left behind; tree ring data shows a cooling between about 1343-1345ish, ice cores from Greenland and Antarctica show that it was massive as well as showing it was near the equator because the amount of ashfall shows they are about equal in amount, with a little less in Antarctica, thus equator. Now, a forest gets cold and grows slowly, no one cares. But crops are plants too, and people do care about those, and the reduced sunlight stunted their growth as well. And places like Germany, France, and the British Isles started to show a marked downturn in yields. There were reserves in these places as well, but ...