Looking at graphs for buffet margins (like the one above) we see an increase in the buffet margin as speed increases up to a point at which the buffet margin suddenly decreases. What is the cause for this decrease? Does it have to do with high speed flight and the loss of lift due to supersonic flow over the wings?
The same doesn't seem to happen at lower speeds.
(Note: This graph doesn't appear properly if your device is in dark mode.)