Maybe a kludgey workaround for this situatation ... is your flash drive totally braindead (fritzed controller), or just suffering a partial lobotomy(worn out memory area [most likely just the lower LBAs])? If the latter, you can use fdisk to delete the current partition 1(now starting at cyl #1), and set up a new partition 1 starting farther into the addressable area (e.g. cyl #1000). (Then re-format and fresh copy all required unRAID goodies.)
You can do that initial diagnosis by just doing "fdisk /dev/sdX" and then the "p" command. If they succeed, so might you.
[ You can then use
dd if=/dev/sdX of=/dev/null bs=1M skip=NN
for decreasing values of NN to find the beginning of your error-free range. ]
Wish you luck.
-- UhClem "We're all bozos on this bus."