How did you upload to the cloud? If you uploaded from Classic, then only Smart Previews are synced, so the full-size original is not in the cloud, so can't be downloaded....instead a 2048 px jpeg is downloaded. If you want your clients to be able to download full resolution images, you need to get the originals up into the cloud instead of smart previews. Any of the LRCC clients will upload full originals.
Using LRCC on the same system as Classic you can import the already synced images, which is intelligent enough to detect that those images are already available in Smart Preview form, so it will import and sync the originals to the cloud, replacing the smart previews. There's no impact on Classic, and your clients should then be able to download the full resolution files.
Of course, if you are already uploading originals, there's a different problem which we'll need to figure out. The bottom line is that it is possible for full size files to be downloaded.