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Generally, this can be attributed to a colder winter. If there is growth starting, then it will likely return with some time. You can recondition the soil with some dolomitic lime, and wettable sulfur. This will ensure that the soil is at the proper pH, and free of infection.

I suggest you pot it up now if it isn't going to be planted in the next few weeks. Often, container grown plants are root-bound by the time they are purchased. If you pot it up now, you can wait until fall to plant, if you wish.

A dense outer foliar canopy will shade the interior and dis-allow foliage to grow in the interior. So it may be normal.
If you think it's excessive or if the outer foliage begins to be affected, inspect closely for insect or mite pests on the stems and leaf surfaces top and bottom. For this you may need the help of a professional for definitive diagnosis and treatment.

This results from damage to the roots from severely fluctuating moisture (repeated drying out and getting waterlogged). Spread 2 to 4 inches of organic mulch on the soil over the roots to avoid this problem. Be sure and plant barberries in soil that has sufficient organic matter in it that it drains well, yet retains moisture.

Without knowing the type of pest you are dealing with I would recommend Neem Oil.
These links will help you.
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
https://www.gardeningknowhow.com/ornamental/shrubs/barberry/barberry-shrub-care-tips.htm

What kind of fungicide was this? Sulfur fungicides tend to be a little less damaging to some trees and shrubs. Copper fungicides can kill trees if applied to heavily.

If this is an area where water naturally runs to, then it could have been over concentrated in that area. Why was the fungicide applied to the lawn? Did you see signs of infection? Applying copper fungicides for preventative maintenance is not recommended.