Based on your post you are having success growing most of your plants. I don't believe you are doing anything wrong.
It is possible the cultivar you have is slow to flower. Some Angel trumpets share this characteristic. If your passionflower is vigorously growing its possible you are dealing with too much nitrogen and not enough potassium.
If most the plants energy is producing new stems, leaves and shoots,it may not have enough energy to produce flowers. Again, less nitrogen and more potassium may get your vine to flower.
A soil test may reveal the answer. Inexpensive kits are available at Home Improvement stores.
