Only some of the buds stay so the blossoms are very short and some are missing the middle. I have been waiting for 8 years to get flowers on these wisteria. I have 3 and they were not all bought in the same place.
Why Are the Little Buds Falling Off the Wisteria Flowers
Certified GKH Gardening Expert
Malformed flowers come from the same reasons as no flowers on a wisteria. I suspect that the plant is getting too much nitrogen. If you follow the directions in this article for getting your wisteria to flower, it should also correct those malformed flowers: