If you are using a cheap USB flash drive (e.g. 2TB USB 3.0 flash drive which cost $8) then the USB Flash drive is obviously a FAKE!
It may report it’s size as 2TB (or whatever is expected – 128GB, 256GB, 512GB, 1TB) but it probably contains only a few GB of slow, faulty flash memory!
You can test the USB drive by filling it full of mp4 video files and then playing the first and last ones, or you can test the USB drive using FakeFlashTest or H2TESTW. See here for details.