I am sure there are all sorts of geo engineering experiments going on putting all sorts of things in the atmosphere from naively haphazard to nefarious, (and the nefarious people will not want you to see it). 99%+ of what you are seeing is vapor trails from just regular aircraft. One leaving a trail and another not is because they are at different altitudes. The temp and humidity can vary greatly from one altitude to the next. You might have noticed something similar if you ever took a tram to the top of a mountain and realized it was colder up top. That was only a few thousand feet and we are talking tens of thousands of feet with the airplanes. Also it is a very finely tuned set of circumstance that leave these trails. This is why one day they linger, the next they quickly disappear.
www.flightaware.com is a website you can see most of the airplanes above you. If one is leaving a trail and the other is not I would check the altitude. Sometimes just a few thousand feet will make a difference.
Here is an example of another display of vapor that is EVEN MORE FINELY TUNED. It's not the same thing same thing but it will give you the idea of something atmospheric that is very finicky.