I am a Banker...
I work at a small community bank and we have experienced this coin shortage. We would order boxes of rolled coin and get 1/5 of what we ordered. I think there are several things causing this.
The flow of coin works like this...
1. Mint manufactures coins
2. Coin is distributed to Federal Reserve Banks
3. Boxes of rolled coin is distributed to large banks.
4. Large banks distribute boxes of rolled coin to smaller banks and retailers.
3. Coins flow between retailers, banks, consumers.
4. Banks and retailers sell coin back to up to National Banks and Federal Reserve Banks who sort and roll the coin again.
What I think caused this issue is a sudden decrease in consumers spending coin and also the fact that bank lobbies were closed for several months. Most people exchange large amounts of coin for cash/deposit in bank lobbies. Without this option, coins quit being turned in. Just our small bank had been selling back thousands of dollars each week in coin and suddenly went weeks without selling anything.
We were still having demand for rolled coin by the retailers that bank with us, but we were receiving none back. If this was happening at banks all over the country, (I am quite sure it was) this created an imbalance in the circulation of coin.