FreeBSD 11.0-STABLE #0 r310265 amd64 seems to be cpi-ing garbage to mounted FAT32 fs after 10-20 GB.

Wed Feb 1 13:18:32 UTC 2017

On Wed, Feb 01, 2017 at 06:02:45AM -0700, Jakub Lach wrote:
> Yes, it has happened also with another device. Which was not a card reader
> (HDD 
> mounted by USB), and I have used the same card reader configuration to copy 
> the memory card content with iMac.

Is your card reader USB-attached, same as the HDD you mentioned ?

Test with UFS filesystem put onto a card or HDD, does system read garbage
or panics due to metadata inconsistency, under the load ?