Have you checked to see if it's fake?
No-brand USB sticks and flash cards sold online are rife with fraud, as well as some fake name-brand stuff sold in retail stores. The cheat is firmware on the device that reports a larger size to the computer than it actually has flash memory for.
Everything looks good at first, but when you try to write past the end of the actual flash, it either (a) errors out, (b) wraps around and corrupts the filesystem, or (c) silently drops the extra data.
There are tools you can use to verify whether such a device actually has the capacity its firmware claims. You can do it by hand, too, but that's fiddly work.
I like `f3` - "Fight Flash Fraud" or "Fight Fake Flash":
https://fight-flash-fraud.readthedocs.io/en/latest/introduction.html
