Random name resoluton problems on L2TP with IPsec

It seems we have a problem about name resoluton on L2TP with IPsec clients connected.
Users are connected using 580 Peplink L2TP “Remote User Access” functionality: our DNS server is and resolves all internal names on a network.
After VPN connected, sometimes users can RDP connect on their PC using name (e.g.: PC0345MI.mydomain.com) but sometimes they cannot: PC is not reachable using name and they are forced to use IP address.
Some suggestions ?

When you do a “nslookup” from the command prompt (cmd) for those connected L2TP with IPSEC client, what is the DNS server shown ?


I resolved using Microsoft’s RDP Gateway.
Many thanks.