Thank you for contacting Ask Extension. Leaf curl is a common problem, particularly early in the season. There are several potential causes for viburnum leaf curl. I think that the best bet is aphids or downy mildew.

Snowball aphids (Neoceruraphis viburnicola) most often occur on European cranberry bush and snowball viburnums. They can cause twisting and curling of the young growth. These aphids are gray to dark green and feed in clusters at the tips of the branches, causing leaf curl. Look for honeydew and sooty mold. Large shrubs and trees usually outgrow aphid damage during the growing season because beneficial insects reduce aphid populations below damaging numbers. The aphids may be gone by now and there is really no need to treat them unless leaf damage is extensive. There is more on aphids at https://extension.umd.edu/resource/aphids-trees-and-shrubs and also help you to identify them. You can use Neem oil to control the aphids, but at this time I do not see any in the pictures that you sent.

Another possibility is Downy mildew (Plasmorpha viburni ). This presents as leaf curl with leaf spots are first yellow then brown. The spots may be angular or have feathery edges depending on species of viburnum. Fuzzy, grayish-white areas of fungal growth may be visible on underside of blotches. The spots may coalesce into large blotches. The leaves become distorted and in severe cases, infected leaves may fall. There is more information on Downy mildew at https://apps.extension.umn.edu/garden/diagnose/plant/deciduous/viburnum/twistedcurledleaves.html

Be advised that horticultural oil should not be applied when temperatures are above 85F degrees, and over application of insecticidal soaps can sometimes burn leaves.

Viburnum leaf beetle can cause leaf curl but there should be holes eaten in the leaves and some leaves should be skeletonized. Make sure that you see these beetles before trying to manage the Viburnum Leaf beetle. If you do see, use Spinosad or permethrin, but it’s important to follow label directions and consider the impact on non-target species.

Cold damage may also cause leaf curl early in the season but it is a bit late for this to be an issue. Even though we did have a last cold snap that could be the cause.

Finally herbicide damage should be considered. This would be from wind drifting of herbicides sprayed in the nearby vicinity, but this is unlikely to be a repeated issue. There is more info on herbicide damage at https://extension.umd.edu/resource/herbicide-damage-trees

Since you did have this problem before, I am not sure if you replanted in the same location? If you did, that could be why you are getting the problem again. It also appears that this area is shady. Viburnums do like some sun to flower. If it does not get at least 6 hours a day, that could be why the amount of flowers were reduced. I also included the MSU Diagnostic lab's info. https://www.canr.msu.edu/pestid/ You can take a sample so that they can accurately determine the problem. 

I have included a publication for future reference. If we can be of further help, let us know.

https://hgic.clemson.edu/factsheet/viburnum-diseases-insect-pests/