A resilient U.S. economy and cooling inflation fueled an intense year-end bond rally. Now, some suspect investors are too sanguine about the months ahead.

The rally marked the latest in a series of swings that sent the yield on the 10-year U.S. Treasury, which falls when bond prices rise, leaping and diving throughout the past 12 months. Fears of a prolonged stretch of higher interest rates repeatedly drove the yield to decade-plus highs, only for stress on the banking system and a Federal Reserve pivot to drag it down again.