Certified GKH Gardening Expert
Most likely. Look closely where the graft meets the desired cultivar. Does it look like branches from below the graft are overtaking the branches above the graft? You can try pruning them out if there aren't too many. Try not to remove more than 1/3 of the branch structure at one time.
This can easily happen when you don't think about checking for it. Each spring, check below the graft for any sprouting branches and remove them.
You can also check for a nutrient imbalance. A soil test will help. Your local extension office can do that for you.