I've found it to happen much more frequently than that, unfortunately. Usually it's because the modal is two DOM elements - a backdrop, that fades out the rest of the content and sits on top of it/prevents interaction; and the actual consent modal. Websites then use various mechanisms to prevent scrolling. uBlock is often only removing the actual dialog, so you end up with a page you can't scroll up or down and can't interact with.

If you're going to turn the filters on, it's worth being aware of this because it's far from flawless.