I have tried to use wiedehopf’s strong message ratio to reduce overload. For several weeks, 40 managed to keep this ratio just below 5. But in the past two days, my message rate appeared to get very low even during times when I normally see high rates. Then I checked strong message ratio again yesterday and today. It went way above 8. At checked times, there were plenty of far away planes within my normal range so this was not a statistical fluke. Today, I reduced gain to get the ratio below 5, and message ratio went back up.
Traffic in my area has been quite stable, which can also be corroborated with several other observations including various global track maps and a second station that I am testing. What could cause this change? Heeshung hinted that an accidental drop of one ProStick may have caused a surge in signal strength. But in my case, my Accidentally Dropped® 
blue stick is the one powering my test site; the stick that suffers from this increase in strong signal ratio is totally safe.
What could be the cause?