OK, devices changed since the diags you've posted, it was sdc:
Oct 7 00:12:30 STORMWATCH emhttpd: WDC_WD30EFRX-68EUZN0_WD-WCC4N1PYS69N (sdc) 512 5860531055
It confirms that the partition is damaged, easiest option it to rebuild the disk since Unraid will recreate the partition, stop array, unassign that disk, start array, post new diags.