I can usually pinpoint the moment someone's Kettlebell Snatch (KS) is breaking down; usually even before they know it. Because the KS is such a complex ballistic movement it's easy to "build in" problems into the technique without knowing it. Issues can build upon one another, and often do, because a fundamental aspect of the technique is not sound or hasn't been developed sufficiently.
In the case of the KS, a technique that everyone wants to do, the key factor in your success or failure is going to be how efficient and effective your backswing is. If your backswing doesn't allow you to load the mechanism to generate power through the hinge then you are going to do it somewhere else. Where you might ask? How about in your hand, arm, neck, shoulder or your upper or lower back. All of these areas are not primary force generators - but they will have to be if you are not using the backswing.
Take a look at the following short video. In it I'm doing a KS with three different kettlebells. What I want you to look at is not only the backswing on the loading phase but also on the recovery phase. They should be so similar that they are almost impossible to tell apart.
If you want to improve your KS then work on your backswing first because where you start (the backswing) will directly effect where you end up (the Kettlebell Snatch).