This looks to be a 512GB Micron 2400. How fast are you downloading? This drive uses QLC and at this capacity (which is low) the cache is pretty small and QLC performance will be pretty terrible. To ballpark it, this flash is rated for up to 27 MB/s per die and you have four dies here so a max of 108 MB/s. Most likely Micron went with a full-drive SLC cache here, so it'll be folding once you exceed that cache at <54 MB/s. I'd estimate it could be even in the 20-40 MB/s range, depending on other factors, which I guess you can check in Task Manager. It's possible your Internet connection is faster than the drive in this state, basically. I haven't seen this drive tested for sustained writes so am not sure how bad it would be, but that's my guess.