Water welting. Too much water will keep oxygen from roots. Only let weather water unless extreme drought. 1-2 weekly waters is max for newly planted cherry trees. Once it’s 1-3 years it may need more.
Yeah waterlogging is usually what causes sudden leaf drop like that on a young tree. Roots can't get oxygen and the tree shuts down fast. Worth checking whether the soil drains properly once it dries out.
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