There was certainly some risk of volatility associated with the G20 summit over the weekend, even if no one expected it to produce any fundamental changes (either in the global economy or the market-based response).  For such things to transpire, we'll need to see more substantive progress and a lot more TIME.  The weekend's headlines concerning a trade war truce (and reopening of trade talks) between the US and China weren't entirely surprising, but they were still worth some bond selling in the overnight session.  

Things may have ended up even worse had it not been for economic data weakness and a subsequent bond rally in Europe.  German 10yr yields surged to new all-time lows by the end of the European trading day, and that was the biggest positive input for US bonds.  Apart from that, ISM Manufacturing was mixed, with a stronger-than-expected headline mitigated by weaker internals.  

Without the benefit of the European risk-off trade, US bonds weakened again heading into the afternoon, but yields remained well within the consolidation range we've been tracking.