What are you migrating from?
If another Mac, are you sure that the OS is as up to date as it can be?
You may need to run Disk First Aid in Disk Utility to make sure there are not any error which can cause possible issues with migration.
If it is migrating from a Time Machine backup, again, run disk utility on it to make sure there are not any disk errors.
If you are doing a Mac to Mac migration, how is it being done, direct connection, ethernet, WiFi. If ethernet or WiFi (especially WiFi), any network disruption could bork the whole migration process.