Windows copy isn’t ReFS block clone API aware , so when you copy REFS data it reinflates and you loose the space savings 🙁 

3 Methods to do this 

1) GSRichCopy360 Enterprise @ 180$ utilizing their Block Level copy with their Rich Transfer Agent

2) Clone Drive using Storage Replication Windows 2016 Storage Replica and ReFS Volumes – Virtual to the Core

3) If its Veeam data , start a new backup chain.