The VM having 3 disks with the same now is only a non-issue due to them being on different datastores (and different sub-directories) - when you migrate them to vSAN they are all in the same namespace and the 2nd one to start copying should fail (*should* get an error or log message indicating file name already exists).
Change the names:
You could easily validate this as the cause by trying XSvMotion of just disk 1, 2 & 5. then trying to XSvMotion either 3 or 4 (or even just disk 1, then try disk 3/4).
That being said, this is a relatively large VM so there is more potential for vMotion failure due to timeout/access disruption so XSvMotion of some disks at a time may be a good idea regardless.
Thank you for the reply.
Unfortunately my vsan hosts do not have access to the old storage, so I cannot migrate a few disks at a time.
I'll look into the kb