I had exactly the same symptoms, not with a USB stick, but with an external NVME drive connected via USB. I discovered that when I asked Windows to give me the used space, that figure did not match the individual folder sizes added together. It would slow down, pause, start transferring again etc. At first I thought the external NVME enclosure was faulty so I bought another one, no improvement. The strange things was that scanning the drive for errors (just using the Windows tool) reported no problems.
At the time, I also discovered that I was getting a lot of WHEA errors (visible in HWInfo, about three WHEA 17 errors every second) and after a fresh install of Windows and reformatting of the NVME drive and it has been fine since. No more WHEA errors, nice fast transfers.
So, it's odd that you have more than one USB stick behaving this way, but check for Windows WHEA errors - perhaps they are corrupting the drives. I never did find out why they were happening, but after I reinstalled Windows for the 2nd time, no more errors. I'm assuming that it was a corrupt Windows driver.
Regardless of WHEA errors, also try reformatting one of your USB sticks anyway and see if that fixes the problem. Hope this information helps...
I also have a question, I was looking at getting a DataTraveler Max. Would you recommend them? Are they as fast as claimed (when working)? Thanks.
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