How old is it?
Is it indoors or outdoor?
Are the root in a shady spot?

How old is it? How do you prune it? Is the main stem getting sunshine? Be aware there are less bees about too. Due to bad weather and fewer hive bees. Grapes show flowers early and pollination takes place early on too. Prune your grape back to main stem in late November whether inside or out. If inside the root is better outside to get adequate water and elements to the root system.