Great question. There really hasn't been many good alternatives to the US stock market. It has outperformed most other markets in the past year.

Treasury yields were down notably today. When bond yields go down, the price goes up. Which signifies money moving into bonds (aka safer assets.) That is likely where big funds moved some money the past week and today.

My guess is that people are also selling and increasing their cash positions for the time being - but I'm not sure how to back that assumption up with metrics.

The question of how long I have even less of an answer for. If I knew that I would be a lot richer haha. My guess is investors are trying to wait September out, and wait for some good news in early October. That could come from Q3 GDP or October unemployment. But the waiting game could go for many months. With winter approaching, investors are worried COVID cases will increase as they did last year