At some point or RPM the air fuel is burning all the way back to the reeds the longer you run at that RPM the worse it will be I have seen it burn back down the transfers all the way to the bearings in the lower end.
I have no idea at what RPM this happens, think back when you were cruising at a lower RPM for extended periods of time.
I have seen reeds where it actually burned the the tips and have seen the rubber on the reed cage burned at the tips.
Ever notice if you take off from a standing start and accelerate real slow you reach a point where the
Engine comes up on the pipe and you feel that surge in power, I never had the problem of burning back to the reeds on any of my engines because I am never at the same RPM for very long, but I always assume it was happening sometime around the time you feel your Engine coming up on the pipe.
Remove the reed petals and wash them off real good with carb cleaner or soap and water inspect them real close take some more detail pics, look for any damage if they show any signs of wear but no chipping or damage then flip them over and run again.