I think a possible explanation for some trails lasting longer than others is that the atmosphere varies in temperature and sometimes pockets are created where it's really cold in one area and then not as cold next to it, also the higher you go the colder it gets so some of those planes may have been lower and the others higher and then the cold air holds it longer in the air.

If you can find footage of two planes like side by side each other at the same elevation leaving dissimilar trails that would be a lot more compelling. However, not sure how you could do that without doing a controlled study and a controlled study of that sort would kind of defeat the purpose.