Did you try replacing the patch-cables and/or SFPs on the path
between servers and disks, or at least cleaning them? A speck
of dust (or, God forbid, a pixel of body fat from a fingerprint)
caught between the two optic cable cutoffs might cause any kind
of signal weirdness from time to time... and lead to improper
packets of that optic protocol.
Are there switch stats on whether it has seen media errors?
zfs-discuss mailing list