I ran a test to reproduce the issue that you are seeing with this Pantone color (377 C); please see the attachment. I was not able to discern any banding in the color in my output. Note that this was produced on 3M IJ40C media, using a custom profile at 120 percent ink limit.
In many cases, it is more difficult for ink to bind with glossy vinyl media than matte media, and defects tend to be more readily apparent using gloss. This tends to be true for solvent and UV inksets in addition to HP Latex inks.