Without knowing the species you have, it's impossible to say for certain. Caveat aside, "sports" are not uncommon among certain passiflora types. Passiflora caerulea is most famous for this, producing blue and white flowers normally, but occasionally growing vines that have all-white flowers. Cultivation and propagation of these white cuttings has led to the popular "Constance Eliott" white-flowered plant.

The native incarnata also has a reputation for extreme flower variability. Flowers can look very different from year to year, and the same plant can have different colored flowers blooming simultaneously. "Alba" is a white form of incarnata similar to "Constance Eliott." I actually had a single white sport appear earlier this year:

This is what the flowers looked like early in the spring:

And this is what they looked like last year:

{{gwi:1123696}}

Hope that helps!

My p. incarnatas are extremely variable in size and color, also - such an interesting vine!
Sherry