Could be drought stress, could be not enough roots to support the shoots. IF you're caging them, you can use some burlap to shade them. I do that with my grafted apple trees sometimes.
IF I recall right, I used 9-12 inch pieces and only had a bud or two exposed above ground.
Much like grafting apple trees. 2 or 3 buds can support the union. Any more, they start, but may die off.
Also, transplanting could of lost some roots. If in harder soil, wet the soil once or twice, then dig deep with a pitch fork and push up a bit until you got cracks in the topsoil. Then wet again. Gets them nice and loose for less root breakage. Spacing apart a bit better help for less tangles too, if possible to do. Some folks with clay soil put some sand in their soil to make it looser in the nursery bed.
MY local soil and water district sell great dogwood for about 1.50 each. Could make your own and mix a few homeande with a bought one.
Do think you had too much stick above ground there from the looks of it.