I don't have angel's summer dream, but I had the same problem with my Rosalla last year. I am used to small buds dropping sometimes, but these buds would grow to almost opening size before dropping. In fact, one even started coming out of the calyx, then dropped. I think only 2 opened all summer. I hope it does better this year.

My Rosalla did the same. All the buds fell off (from small to large)with only one exception which is in bloom right now. This is the first bloom for this cutting. I'll post pics latter.
Also my double white dropped like 15 buds but fortunately has a few left on it which will open soon. Hope I did not speak too soon. Keep my finger crossed. This is the first time when it drops buds since I had it( about a year).

My ones outside drop a lot. I thought it was due to the high wind so I am keeping some in the greenhouse with a little wind protection so I'll see if that helps any.