Is this a new setup and these LUNS don't have any data written on them ? If yes, Please go ahead and delete the LUNS and recreate and assign them to the host group again...
If NO, May i know what are the steps taken before unmapping it from a individual host groups and mapping it to another host group ?
1. Stop any application on the windows server hosted on these LUNS (Make sure no transactions on the LUNS)
2. Unmap the lun from current host group and map to new group
3. From Windows disk management run a scan/refresh
4.Start the service/application if any