how to troubleshoot slow usb drive?

TLDR: How do I troubleshoot a slow usb 3.1 device plugged into a laptop. ISSUE: When I copy (tried GUI and terminal) the first few .iso files copy almost instantly 300mb/s+, but then the 3rd/4th start to slow to below 12mb/s (even if copying one at a time). HARDWARE: - Dell XPS 15 9520 (Fedora Linux 37 - Workstation) - Sandisk Extreme GO USB 3.1 64GB (using Ventoy) - Dell USB-C to USB-A/HDMI Adapter - Anker PowerExpand+ 7-in-1 USB-C PD Hub TRIED: - Reformatting usb (gparted - exfat). - Using USB with and without Ventoy installed. - Using different ports, different adapters/hubs. - Copying lots of .iso files in one go vs copying one file at a time - waiting until each file fully copied. Either way after a few files (around 4GB) the USB drive becomes very slow. Ejecting the USB (via GUI or terminal) can take a long time but after remounting fast speeds return. When ejecting using GUI I get message device busy - so now use terminal and wait until command has completed. DRIVER | PORT DETAILS:

$ udevadm info -q path -n /dev/sdc

/devices/pci0000:00/0000:00:14.0/usb4/4-1/4-1.1/4-1.1:1.0/host1/target1:0:0/1:0:0:0/block/sdc


$ lsusb -t

/:  Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/4p, 10000M
    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/1p, 5000M
        |__ Port 1: Dev 3, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
/:  Bus 03.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/12p, 480M
    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/5p, 480M
        |__ Port 5: Dev 6, If 0, Class=, Driver=, 480M
    |__ Port 2: Dev 3, If 0, Class=Hub, Driver=hub/4p, 480M
        |__ Port 1: Dev 5, If 0, Class=Hub, Driver=hub/4p, 480M
            |__ Port 1: Dev 9, If 0, Class=Human Interface Device, Driver=usbhid, 12M
        |__ Port 4: Dev 8, If 0, Class=Hub, Driver=hub/4p, 480M
            |__ Port 3: Dev 11, If 0, Class=Human Interface Device, Driver=usbhid, 1.5M
            |__ Port 3: Dev 11, If 1, Class=Human Interface Device, Driver=usbhid, 1.5M
            |__ Port 4: Dev 12, If 0, Class=Hub, Driver=hub/4p, 480M
                |__ Port 4: Dev 13, If 0, Class=Hub, Driver=hub/4p, 480M
    |__ Port 3: Dev 15, If 0, Class=Hub, Driver=hub/4p, 480M
        |__ Port 2: Dev 16, If 0, Class=, Driver=, 12M
    |__ Port 6: Dev 4, If 0, Class=Video, Driver=uvcvideo, 480M
    |__ Port 6: Dev 4, If 1, Class=Video, Driver=uvcvideo, 480M
    |__ Port 6: Dev 4, If 2, Class=Video, Driver=uvcvideo, 480M
    |__ Port 6: Dev 4, If 3, Class=Video, Driver=uvcvideo, 480M
    |__ Port 9: Dev 7, If 0, Class=Vendor Specific Class, Driver=, 12M
    |__ Port 10: Dev 10, If 0, Class=Wireless, Driver=btusb, 12M
    |__ Port 10: Dev 10, If 1, Class=Wireless, Driver=btusb, 12M
/:  Bus 02.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/2p, 20000M/x2
    |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/4p, 5000M
        |__ Port 2: Dev 3, If 0, Class=Vendor Specific Class, Driver=r8152, 5000M
        |__ Port 3: Dev 4, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
/:  Bus 01.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/1p, 480M