There are several, except they usually aren't classified as mass shootings because they are stopped before that magic number of four required is reached. One I remember from a research project years ago was Clackamas Center.
One thing of note, rarely do police officers actually shoot the suspect. Just the threat of armed resistance showing up is enough for the shooter to turn the firearm on themselves. The same happens with citizen carriers.
Gun control advocates love screaming that citizens never stop a mass shooting. That is because they prevent them from reaching that threshold. It makes it hard to show how many have been stopped.