First published by Money Metals here: https://www.moneymetals.com/news/2018/09/20/us-mint-supply-silver-eagle-sales-001621

The sales of Silver Eagles surged in September as the U.S. Mint removed their temporary supply restriction. As the silver price continued to trend to new lows at the beginning of the month, several large purchases of Silver Eagles by the Authorized Dealers wiped out the inventory at the U.S. Mint. The U.S. Mint had cut back on its monthly supply due to the falling demand.