This happens regularly with my Marquette vines. So much that I am replacing them this year. A vineyard operator near Carver, MN told me several years ago that he had the same problem and took out all of his Marquette. He told me it is from freeze damage to the trunk. Most of the capillaries(?) freeze during the winter and when the growth starts in the spring, the vine does not have the capacity to support it and the vine dies.