Problems in the digitization of control point

Guys, I am wondering what does the yellow question marks shown in the top right corner of the photos imply?

Also, the rms of reprojection error is so large, but I try to pick the same location of the point in each picture, why it will have such problems?

Are there any techniques in the digitization of control points?

Thanks, guys, it would be big help if you have any suggestions!