DanMarian is correct; another downside to UG filters in planted tanks is the faster (relatively) flow of water down through the substrate. There is a natural flow of water down into and then back up through the substrate in nature and in planted aquaria. This serves two main purposes. First, it brings oxygen rich water down to the aerobic bacteria [more on these in a moment in connection with your plant debris issue], but more importantly it brings nutrients to the plant roots, and that is essential. But the roots need some time to assimilate the nutrients, so a faster flow through the substrate is somewhat detrimental.
To the debris. This I suspect is mainly the rotting leaves of the Wisteria, which can accumulate I know. When this is excessive, they should be removed during the weekly water change. But normally, debris is allowed to settle into the substrate, and that aerobic bacteria mentioned earlier breaks down the organics into useful nutrients for the plants. There is quite a complex biological process going on in a healthy substrate. In planted tanks the gravel should not be deeply vacuumed but left alone, just skim off the surface debris in open areas when it is excessive.
Back to the dying Wisteria; are you using any fertilizer, and if so, which one? And what is your light (type, be specific) and duration? And the tank size (volume)?
You mention other plants doing well, which species? This may give us a clue.