Distinguished SOTW Member
I noticed this too on my clarinet reed.There is also something weird about the intonation when using this reed for a longer period of time. It works ok for an hour or two but than it seems to be harder to control.
I think I read something about this on the box or online when I got my first Euro clarinet reed. Apparently the performance of the reed changes during extended practice sessions. It seems to go back to normal the next time I play, though.