They need to be in sun, and they need training and pruning - see link below

https://www.rhs.org.uk/advice/grow-your-own/fruit/grapes

When growth starts again make sure you feed it - sounds like it is lacking Potassium - I had the same trouble when I 1st started to grow them outside.

And not to forget to prune and train

I would also try to find out which variety it is, Thingummyjig. Some kinds need a heavy pruning of last year's growth every winter (spur pruning), while some need to have some of the canes left long to produce fruit (cane pruning). Chopping back a cane pruned variety will stop the fruit pretty efficiently.