I'm not sure why the user is experiencing this issue, but here are few things to try:
Check which groups are included in the users access token when the user is logged on both machines run whoami /groups
, specifically check for denied groups
Connect to the network share directly and not via a drive mapping i.e. \<server_name>\<share_name>
Connect to the network share directly via the IP address, which will bypass Kerberos and use NTLM i.e. \<server_ipaddress>\<share_name>
Gary.