10yr Treasury yields jumped at quick 3bps starting right at 8:20am. That's the official opening bell for the CME trading pit, and the unofficial open for true liquidity in the bond market. That means it's frequently a time of day where trading activity surges. That can be especially true for mondays (traders who took positions to neutral over the weekend getting back in the market) and the 1st trading day of any given month. We can include the 2nd trading day of any given month when it happens to be a Monday.
One of the sources of additional volume and momentum at this time of morning can be the announcement of new corporate bond deals. In today's case, we had a big one from Apple. Corporate issuance typically adds negative pressure on bond markets.
MBS have been pulled down at a similar clip with 2.5 coupons off nearly an eighth of a point already. 2.0 UMBS coupons are down 6 ticks (.19).
All of the above having been said, everything looks to be stabilizing now.