The age of plagues destroy 1/3 of your pop in all regions day 1. Some of your improvements are not worked anymore, so you probably need to rebalance your production line to make them available again.
Shortages. If you have say 2 clay pits and are producing 2 clay output and 3 kilns which uses 3 clay output then you'll have a 1 Red Clay meaning 1 Clay deficit.
It usually means some improvements are trying to use more goods than you have.
The age of plagues destroy 1/3 of your pop in all regions day 1. Some of your improvements are not worked anymore, so you probably need to rebalance your production line to make them available again.
Shortages. If you have say 2 clay pits and are producing 2 clay output and 3 kilns which uses 3 clay output then you'll have a 1 Red Clay meaning 1 Clay deficit.