After checking the Windows Spotlight API, the path $.batchrsp.items[@random].item contains a string that is JSON, where the image is contained.
When using $.batchrsp.items[@random].item.ad.landscapeImage.asset, the image is not retrieved because the string is not JSON itself, it has to be parsed first.
A way to fix this is to allow the JSON string to be evaluated as JSON by enclosing the string path with {} (or any other alternative).
$.batchrsp.items[@random].item:{$.ad.landscapeImage.asset}
This would also fix any offending API that returns a JSON string.