I don’t play particularly loudly, but I find a certain few reeds tend to fail first. These are ones that tend to come up a lot in the tunes I play, and they’re around the 3rd F sharp on the P37D.
You know when a reed has failed because it rapidly drops 20-30 cents. If you tune it back up, it rapidly drops again and eventually snaps. When I hear this happening now, I replace the offending reed plate straight away.
Many harmonica players have learnt to remove the rivet that attached the reed to the plate so they can fit a replacement reed. This saves the cost of a whole new plate for one faulty reed. There’s a few youtube videos explaining how to do this. I haven’t tried it yet, but I will soon.
A video from Hohner: