I don't know if anyone else has had this problem, but the flower buds on my two Stella Cherry trees have only the green sepals when they open and no white petals. They are in a fruit cage so it can't be bird attack and they appear to be healthy otherwise. I had the same problem last year. I bought them both about four years ago and have been fan training them from whips. Is it possibly a genetic problem as they both came from the same supplier?
I am having the same problem with my Stella, so I hope someone has an answer. Mine not only are missing the white petals, they also have no pistol or pollen... just what looks like small black dots on the inside of the sepals.
I'd get in touch with the suppliers straight away. Also take very good close-up photos.
Same problem here in Quebec. Not only with Stella. Bing and Lapins exhibit the same lack of flowers. Buds kinda opens but with no white petals. I am so sad First year it happens. Romeo, Juliet and Montmorency are full of flowers. Seems to be something with the sweeter varieties.