It's hard to diagnose without images of the symptoms and how extensive they are (although, to be fair, sometimes symptoms aren't distinctive enough to confirm a diagnosis), but Japanese maples often develop dieback in small twigs or branches, especially if stressed by drought or injured in a late winter cold snap, like we had this year. For example, trees stressed by roots getting too dry or by a summer heat wave can be vulnerable to opportunistic infections like Botryosphaeria canker, a commonplace fungal disease that can kill branches.

Regardless of the exact cause, the only recourse once dieback appears is to prune out the leafless branches or twigs, as a fungicide application won't provide any benefit and can't cure existing disease (assuming a fungus is involved at all). If the tree is being shaded more by another, taller tree nearby, that could also lead to a natural thinning (leaf shedding and eventual branch death) of the canopy interior, since it's getting less light over time.

For now, other than pruning off branches that never leafed-out this year, all you can do is to monitor the tree for watering needs since the drought Maryland has been experiencing for around two years now has not yet abated. Our Watering Trees and Shrubs page has guidance, if useful. By late spring, if any more branches have not leafed-out along with the rest of the canopy, they can be pruned off at that time so they don't harbor fungal spores or wood-boring insects.

You can also inspect the branches for Japanese Maple Scale, which is quite small and blends-in to the bark very well (they won't be found on leaves), and if present and abundant, then you may need to hire someone to apply an insecticide to control them. High populations of armored scale like these can contribute to branch dieback, and despite the name of this scale species, it can feed on a wide variety of tree and shrub species, so it would be hard to tell where it originated in that case.

Miri