There are two possibilities here. The first is that the loop was properly built, and the kinks developed over time when the track shifted on the subgrade. The second, and we won't know the answer to this until after the survey, is the subgrade itself is substandard in some way. The fact that the loop was successfully used for many years hopefully suggests the former, and that the fix will be reasonably simple. Admittedly we are being super conservative, but don't want to take any risks with our equipment or people.