If these USB sticks were purchased from eBay or at a street market, it is quite possible they are fakes, especially if they claim a high capacity (e.g. 64GB+) with an unusually low price tag. The fakes typically come with 2GB or 4GB of real capacity with modified firmware to look like their claimed capacity, so the user is fooled into thinking the drive is working and in the case with eBay, gives the buyer positive feedback.
However, once the real capacity is used up on a fake product, the drive effectively self-destructs, usually by overwriting existing data or losing it by trying to write to non-existent flash.
If you have another USB drive bought from the same place/seller that still works, have a look at this link for a utility that tests the drive.