If there was a specific catalyst, it was Powell saying they've been watching the run up in rates and it's nowhere near where it was a year ago. This is true, but bonds don't love hearing it.
MBS are now up only 11 ticks (.34) but that's down 6 ticks (.19) from the mid day price plateau. 10yr yields are up to 4.374, still down 6bps, but more than 3bps up from pre-Fed levels.
