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Yes, you can go ahead and try root pruning now. Bone meal is fine for adding more phosphorus to the soil. Here is more information: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/bone-meal-fertilizer.htm

Unfortunately, it sounds like it may have crown rot. The white patches are likely lichen, which are more of a side effect of the ill health of the plant. They tend to attach to woody plants that are dying. This article will explain more about crown rot and does have some suggestions on how you might be able to help your vine: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74133.html

It sounds like transplant shock. It can happen sometimes to plants. This article will help: https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm As for the soft soil, there may be a few air pockets in the soil contributing to the shock. Step firmly around the plants to collapse any air pockets and flood the area with water to help fill them in.

You may want to consider adding some phosphorus to the soil, like bone meal, which helps promote blooming. This article should also help: https://www.gardeningknowhow.com/ornamental/vines/wisteria/wisteria-blooming-problems.htm

I would guess that the nitrogen to phosphorus ratio is off. The soil may have an abundance of nitrogen, which would result in nice, healthy green growth but little to no blooms. Without the right amount of phosphorus, it will not bloom well. Bone meal is a great way to add phosphorus. This article will also help: https://www.gardeningknowhow.com/ornamental/vines/wisteria/wisteria-blooming-problems.htm