Hi Jo. That could be due to a variety of things. I would take a look at the base of where the symptoms are starting and see if there was possibly any damage along the vine somewhere that may have cut off water movement. Possibly an insect feeding on the vine or mechanical damage.
The other possibility could be a root issue that may be limiting water movement as well. If you dig up any of the root system and the roots do not look white and healthy, that may be a sign of a root rot issue. That is possible with the over abundance of rain some areas in the north have been having. Check out those possibilities first and see what you can find out.