Are you sure the ssd is a real ssd and not one of the fakes that tell the os they are so-and-so big, but they’re really a small capacity drive with custom firmware that overwrites data when it gets full.
What does df tell you after you do the initial installation.
What happens if you try filling the available space with something else:
dd if=/dev/zero of=reallybigfile bs=1M
That will run until it runs out of storage space. (Don’t worry – it will tell you when that happens and stop running at that point.
ls reallybigfile and see how big it really is, i.e. how much space you really have available on that ssd.
Now rm reallybigfile.
Does everything still work? Is the os corrupted again?