In general SNAP 6 has bug with sen2cor 2.8 according to the Source of the post
But I applied it from the cmd, and successfully implemented and got the results,
I also applied sen2cor 2.5 to your product and I got same results as you have,
As you see applying both sen2cor 2.5 and 2.8 don’t change the result, I’m curious now to know the reason,
The reason of the datastrip might be explained in here,
Source: https://sentinel.esa.int/documents/247904/685211/Sentinel-2_User_Handbook
But I also now wants to know the reason of this result,