Why can't files from a flash drive open?

Question

USB flash drives

There is a flash drive from China on 64Gb. If you write files to it one at a time, then everything is fine. If you record 3-4 files at once, for example, photos or movies, then they will not open later. The pictures show a black screen, and the movies start and the time is counted down, but the gray screen is silent. Tried to format in NTFS, exFAT, tried different sizes of clusters, the problem was not solved. With other flash drives, this problem is not observed.

Answer 1

Two options

• the volume of the flash drive is not 64 GB at all, and only part of the information is recorded (h2testw for verification)
  
• the flash drive's firmware does not work well when writing to random LBAs, and only sequential writing works fine (I've never seen this)
  

Answer 2

Most likely, the real volume of 4 gigabytes is a frequent occurrence in Chinese flash drives, there are also 4 such flash drives.
I re-partitioned it to 4 gigabytes and I use it.