You did a Backup-2-Master in order to decommission the previous master server. Once done you can not access you file shares any more and your data appears to be lost.
During the procedure only user data is transferred and role attributes of the servers will get changed. The data itself does not get copied and the shares are still configured to be activated on the previous master.
Create new shares on the new master server and copy (ie with rsync) the files from the old master to the new share on the new master.