Bought this kingston xs2000 a while ago. It's officially rated for "up to" 2000Mb\s read\write but slows to a crawl after 30GB have been copied. Fyi, I'm copying files from an internal nvme (samsung 980 pro) via a usb 3.0 cable, so this kingston ssd is the only bottleneck.
I agree with the other comment.
https://www.techpowerup.com/review/kingston-xs2000-2-tb/2.html
The drive has no DRAM cache, 99% chance that it is using a portion of the flash as SLC "cache". When the cache fills up it has to write it out to TLC storage.