The judges usually change jobs from prelims to finals. And, most judges also have their own preferences in their grading of bands and the type of show they like. So what we saw with Vista from prelims to finals could easily be a switch as music judge J2 in prelims became marching judge J5 in finals, placing the band they saw as 7th in marching at prelims as 9th in music at finals. It isn't as noticeable, but in Westlake's scores, they placed 4th in both marching judges' scores from prelims and then in finals got three straight 4th's from all three music judges. I agree that Vista's 7th and 9th scores weren't really accurate, but this should help explain that it was probably just one judge who gave both scores, and they probably just didn't prefer Vista's show over the others they saw.
Also, congrats to all four bands advancing to state!