I have lately been copying large amounts of large files between drives lately. I have a SanDisk Ultra 128GB USB 3.1 (claimed) Dual Flash Drive and a Transcend 2TB StoreJet External Hard Drive. It is worth noting that the flash drive is brand new and the hard drive is a few years old. My computer contains a 1TB Samsung 960 EVO NVMe SSD which is the drive I am transferring from. The test I ran involved copying about 65GB of video files to each drive (the same files for both devices). I started the write to the flash drive a couple minutes before I started writing to the HDD and the HDD finished far and away first. The HDD sat at a fairly constant 124 MB/s, while the Flash Drive hovered wildly between 32 and 43 MB/s. I know the Flash Drive can do more than that because when I transfer only one or two large files, it starts over 100 MB/s, then drops down to the aforementioned wild fluctuation. It does this whether I use the USB-C connector or the USB-A connector. I have tried changing the caching setting, and it doesn't do anything. Both of the other flash drives I tried (a Transcend and a Microcenter) showed similar issues. All of them are at least USB 3.0. The Transcend was basically identical to the SanDisk and the Microcenter ramped up to about 30MB/s before almost immediately throttling to under 10. I'm sort of at a loss here and I'm very unsure what's going on. Any help is appreciated. Fair warning: I'm a bit of a noob. My computer is a Lenovo ThinkPad P71 with an Intel Core i7 7700HQ, 32GB RAM, 1TB 960 EVO NVMe SSD, 1TB HDD, and a Quadro P4000. It runs Windows 10 Pro.