The reasons for what is happening can be several factors. First, the US Federal Reserve System conducts operations to reduce the balance and withdraws from the market 10 billion dollars every month. Secondly, the American economy is preparing for a large-scale return of dollar liquidity to the country.
Tax reform, started by Trump, aims to return to the US about 2,5 trillion dollars. This is the money of the largest American corporations that keep them abroad to save on taxes.
Today, the global need for dollars is significantly higher than the Fed prints them. Moreover, the recent actions of the American regulator will further reduce monetary liquidity in the markets, which could lead to a global recession.