I don't see how it didn't kill your St Aug last time. It's 2,4-D, Quinclorac and Dicamba. The label states not to use it on St Aug. Quinclorac is a common product used to kill St. Aug in Bermuda lawns. I don't know the viscosity of each of those ingredients, but always shake your bottle well prior to mixing. Could be the Quinclorac separated to the top and that was the heavy concentrate you mixed. But either way that is not a product I would use on St. Aug.
Yes, I see that now in the very fine print. I was more focused on the large print on the front of the bottle that reads "WON'T HARM THE LAWN, GUARANTEED".
If there's any good that came from the experience, now I know what beats Roundup in both price and effectiveness when it comes to killing grass and weeds