In any sVMotion , files which get left out in source and do not move to destination are they ones not in use and are known as Zombie disks.
I suggest , click on browse datastore:
check the date they were last updated , it will be old
Try renaming them , if it allow it confirms they are anyway not in use.
remove it from datastore , again i say if it allows you then confirmed it was never in use.
In my infra it happens very frequently
Instead of svmotion i first try create test snapshot , then delete all snapshot from snapshot manager , it help in consolidation.