Protein in cooked vs. raw chicken breast filet
Proteins are complex chemical forms so it depends.  Let me elaborate by giving 2 extreme examples:


If you boil an egg, the proteins unfold, hook into one another and therefore a liquid becomes a solid that doesn't melt again when you cool it down and there is no protein loss whatsoever.
if you burn a piece of chicken breast fillet to a crisp on a barbecue overnight, a lot of protein mass will be lost. 


In your particular case, I see the following possibilities:


there is an error in the label of one of the products and they probably did not send off their product for actual testing, but took their ingredient list from a database.
the cooked chicken is encased in a batter and the end product just happens to have the  same protein content as the uncooked chicken.


You should contact a local consumer protection program and have them send off both products for actual testing as these kinds of tests are quite expensive.

As your labels are German, I advise: https://www.test.de