These bubbles may appear during the application process, when water or air remains trapped between the window and the film. If the window was not cleaned properly before the application, the adhesive will not stick well and will leave room for air or water.
So the bubbles can be a sign of a poor application of the film, but they also may appear over time, as the tint starts to break down. In our shop we will make sure to not leave any bubbles or wrinkles behind, and even if that happens after some years, we will change it for free. We offer a lifetime warranty for labor, peeling, bubbling or fading.