Saw bright object following then in front of planes.

Going to town my son and I were watching four planes flying. The planes were the high flying airliners, and not some individually owned plane. It was 5:30 pm and the sun was setting just behind the tree tops in front of us. While watching one plane go from our right to left, a shining object appeared behind the plane, at the location where the vapor trail was dissipating. The object maintained the distance as the plane was flying and was there for about 20 seconds. When it appeared it kinda blinked a few times and then was fully illuminated. We watched it and were disappointed when it blinked off. The other planes were still in view and we saw the same thing appear in front of a different plane. This time it just appeared fast and was maintained its distance in front of the plane. It was brighter this time against the blue sky. It stayed in front of the plane for about 30 seconds and then disappeared. I was thinking the sun was illuminating the object because of how the sun was setting and shining on the bottom of the plane. It was definitely something there. It couldn’t have been a star. I’m not sure the location of the iss at the time but that may have been a possibility.