In the overnight session, the rest of the world decided it was just as concerned about the Fed potentially having waited too long to cut rates as some many investors were on Friday.  Japan, in particular, had a rough night with the Nikkei down 12.4%. European indices were down 2-4% and S&P futures fell into the same range. Even crypto was swooning with BTC losing nearly 20% since Friday.  All that money needed a place to go and the bond market soaked up quite a bit of it.  10yr yields were as low as 3.666% at one point and Fed Funds Futures showed a 50bp cut in September.  
The gains began to unravel even before the ISM data came out, but the data kicked the sell-off into higher gear, ultimately completely erasing the overnight progress in both ends of the curve.  That said, most of the post-NFP gains are intact, and we’re still hugely improved over the levels seen before last week’s Fed announcement.