I have been plagued with USB file transfer slowness in Ubuntu since version 10-something. It would manifest as a long delay between short bursts of file transfer.
After reading several forum postings, I never really saw a solution that worked. One suggested adding “pci=acpi” in a startup file, but that didn’t seem to do anything for me. Another suggested that the graphic card and the USB were having a bus conflict of some kind. Then I thought, perhaps the common issue here really is the computer rather than the OS.
Solution: I changed BIOS to disable “legacy” support for USB. Tonight I transferred from two different USB devices and each went through with no delays. The speed wasn’t phenomenal, but the stop-start thing didn’t manifest at all. I’ll still have to try some very large files, but some 100MB files went through fine.
UPDATE: Just transferred some 2GB files from a video camera and there were no pauses at all, and about 9.5MB/sec. I think the BIOS setting is really the root of this issue, though it may have a software component to it.