We use 3M180 profile for EVERYTHING. Banners, reflective (3M 5100), and intermediate (3M IJ35C). We also use 720x1440 and very rarely have issues with black banding. We tried the 540x1080 and it doesn't satisfy us. Leaves a bit of a fuzzy edge. When we print it is a very clean, crisp, print.
But as for your issue, whenever we have banding, I do the feed composition, cleaning, and really try to re-align that media. The last few times have been because the media wasn't aligned properly. Maybe the roll is slightly uneven, causing it to pull differently on one side compared to the other. Hope you get it figured out.