Replying to Look pivot binding din setting loosens by itself

I noticed yesterday that the DIN setting of my look pivot 15 loosens by itself. I normally ride with 8 but after 4 hours of skiing the DIN setting of one of the front bindings dropped down to 5. So I just put it on 8 again. But at the end of the day it was already back at 6. Only one front part of the binding is affected. The other 3 parts are fine. I have no idea what's wrong with my binding. I also couldn't find any cracks or other damages.
I bought the binding this season. I had a few crashes but they were not very heavy.
Do any of you have an idea how i can fix this problem?

(sorry about the bad english I'm from switzerland)