quality issue

Check for sensor spots: 

They are visible when you take pictures against the sky. They are less visible when there is no uniform background. 

To correct your old assets, you can use the stamp filter from lightroom. The spots are always at the same place. 

To correct the issue, you will need to do a sensor cleaning, either by yourself or by asking a professional cleaning service.

I would also edit this blue blob out (first picture). It isn't probably an erro, but it may be disturbing: 

As a general recommendation: I would try to lift the shadows a bit.

The large blown out areas from shooting directly into the sun are probably the reason for rejection. 

You may also have problems with the underexposed shadows, sunspots and the overexposed sun.

Sensor spots for one. You probably also would need a model release. I would just remove the individual altogether. He adds nothing to the compositions