why does the buds turn yellow and drop off before flowering

Sometimes Valerie1 the passiflora foetida that's grown from seed will do this - they do not flower properly. Was yours grown from seed?

No this was not grown from seed but was bought from a nursery. Last year it was covered in blooms and I cut it back in the Winter and it has grown vigorously and has even more buds than last year. One or two are buds are blooming but a lot of them are going yellow and dropping off.

I would very much like to get this sorted out because it is a beautiful plant.

Thank you