SNPs with same position but different informatios

Question

[claudia_io_p]

I do GBS with tassel and my vcf file have a lot SNPs with the same position. And I have a lot of question:

Why do SNPs appear with the same position but different values of NS, DP, among others? What does that mean? And what is the cause?

an example of this:

1   523343  S1_523343   A   G   20  PASS    NS=260;DP=6608;AF=0,46
1   590610  S1_590610   A   T   20  PASS    NS=266;DP=10670;AF=0,01 
1   590610  S1_590610   A   T   20  PASS    NS=275;DP=10713;AF=0,01 
1   592230  S1_592230   A   T   20  PASS    NS=266;DP=12953;AF=0,26 
1   592230  S1_592230   A   T   20  PASS    NS=273;DP=12999;AF=0,26