My ZD is planted on the ground, by an east facing wall and about 3-4 feet away, there is a pergola that provides shade to it and nearby planted azaleas, camellias and hydrangeas. When it gets shade, it is not dense shade but "bright shade". It always blooms well for me so I would not consider the shade that you describe as the causal agent. Perhaps, as mentioned before, the roots are circling and-or perhaps the soil needs more ump fertilizer or moisture-wise. These climbers like to "eat". In my nearby plant nurseries, they sell soil test kits to check nitrogen/phosphorus/pottasium content. They are quite cheap and very inexact but they help me determine when the levels of one of those minerals is either too low or high. You may want to ck on the roots and the levels of minerals to see if either is causing the lack of blooms. A pest here in the states called Rose Midge can also cause blooming problems. So can crown gall.
