Ok lets see this:
# Can you try and do a vmotion of these machines to a different host in the cluster. And then try and do a sVmotion to target datastore.
# Also, check the MPP for the target datastore on the ESX host that presently is hosting the VM.
# last thing I will check for is the FAs presented to target lun on your SAN. If its 2, talk to your SAN admin if he can give 4.
I have done tonns of sVmotion from DMX to VMAX on vSphere and at times found issues ranging from SAN to host to VM for failing sVmotions. Let me know if this helps.