What do I mean when I say 'serendipitous' market movement? In general, this is just another way to say "that's the way the ball bounced, cookie crumbled, etc." It tends to apply to days like today that tick several boxes on the scorecard of irrelevance.
Summertime trading day--especially in August? Check.
Movement happened Monday morning and then fizzled? Check.
Nothing significant on econ/event calendar? Check.
No obvious reactions to news headlines or other intraday updates? Check.
Very light volume and liquidity? Check and Check.
With all of the above in mind, this morning's gains don't require too much investigation. Considering they began right at the 8:20am CME open, we can be reasonably assured that traders were lined up to buy and simply waiting for the green light. Once buyers got their fill, bonds drifted slightly higher in yield for the rest of the day, ultimately ending fairly close to 'unchanged.'
More meaningful events don't show up until Wednesday afternoon, so we could see more of the same tomorrow. Just remember that this random trading action is just that. We improved for most of today, but it could be the opposite next time.