Ground Control Points

Hello, I have a problem when I work with the GPC.
I have 6 GCPs, after I reoptimize the model the offset between the blue dot (initial) and the green dot (computed) is almost zero except for one GCP.
To select this one I used 11 pictures and the quality is very good. I would like to know why I have this gap for this GCP and how I can fix it.