When an instance is removed from a Hierarchical Instanced Static Mesh's array, if there are indices that are further along in the array that fill that index, the last index in the array is used to do so instead of the next in the order.
Example: If you have a Hierarchical Instanced Static Mesh component with 5 instances in it and you remove the instance at index 0, the instance at index 4 (the last one) will be used to fill index 0 instead of index 1.
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This also occurred in 4.13
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