Hmm .. I'm not aware of any changes made to the downloader code.
We are using Cloudflare as content delivery network. They have servers all over the world. If the one closest to you doesn't have the files yet, it has to download them from our source servers first, which might take a little longer. If you now come back to the same download after a few minutes, the file is cached and it should download much faster.
I was mistaken, it seems only when trying to download the newer driver version does it slow to a crawl, specifically at copying installer files, but it's so slow I haven't gotten past that yet. Any version above 472.12 slows it down, and only on 1.10+ does it detect that version to be the best for my hardware. I tried to download them on 1.10 but it did the same thing... Downloading from the nvidia site yields no issues, only when downloading using NVCleanstall.
I dug a little bit deeper and it seems Cloudflare will only cache files up to 512 MB. The "Display Driver" download is 660 MB though, so it will always download from our servers through cloudflare's own network
Edit: guess the solution is splitting that file into smaller chunks, just not sure yet how to handle this in my workflow and also NVCleanstall needs support for it