Remember "global growth concerns?"  That's the phrase that underpinned the rate reversal from long term highs in late 2018.  It's definitely not reliving its past glory just yet, but it's starting to get thrown around again.  Weak Chinese econ data contributed to the sentiment overnight, but it was Moody's downgrade of multiple U.S. banks that did the most to spook the market and drive "risk-off" trading.  Treasuries are always the bigger beneficiary of such motivations relative to MBS and today is no exception.

Same chart through the present day.  Jury's out:

MBS's recent outperformance and today's underperformance.