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This is likely Black Rot disease.
Here is a link with more information.

https://www.gardeningknowhow.com/edible/fruits/grapes/treating-grapevine-problems.htm
https://www.gardeningknowhow.com/edible/fruits/grapes/black-rot-grape-treatment.htm

It sounds like it is a pollination issue. This plant does best with another of its kind planted nearby for cross pollination. They can self-pollinate, but most of the time, the plant will drop its fruit if it self pollinates. A second planting should help both produce full grown berries.

This may be a fungus issue.
I would treat the grapevine with Neem OIl.

I have listed a few links for you.

https://www.gardeningknowhow.com/edible/fruits/grapes/treating-grapevine-problems.htm
https://www.gardeningknowhow.com/edible/fruits/grapes/black-rot-grape-treatment.htm

Well if they're newly planted, you're likely to lose the grapes already on the vine if it becomes stressed from the planting, though it will not hurt to leave both the foliage and fruit on the vine. If you would like information on pruning them back, however, this article will help: https://www.gardeningknowhow.com/edible/fruits/grapes/prune-grape-vine.htm

Check the vines for signs of insects or fungus disease. Treat with Neem Oil if you find any issues, and you may want to use as a preventative treatment.

Be careful to not water the leaves, if your needed to water due to dry conditions, water below.
Occasional drying leaves would not be uncommon as the late summer is upon us.

Review the growing conditions as in the link below.

https://www.gardeningknowhow.com/edible/fruits/grapes/treating-grapevine-problems.htm

https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm

Provided that the grapevine is not too large, you can do this in spring or fall. But please keep in mind that this will not be an easy undertaking, even for smaller vines. Grapevine roots are deep when compared to many other types of plants.

Cut back the vine to 8 inches from the ground. Before you dig out a grapevine to move it, excavate down around the perimeter of the main trunk out a distance of 8 inches or more. This will help you find any peripheral roots and free them from the soil. Once you have the bulk of the outer grapevine roots excavated, dig down deeply in a trench around the vertical roots. You may need help to move the vine once it is excavated.

Lay the roots on a large piece of burlap and wrap them in the material. Move the vine to a hole that is twice as wide as the roots. Loosen the soil at the bottom of the hole to the depth of the vertical roots. Water the vine frequently while it re-establishes.