LAN clients cannot access/ping VPN clients

Dear Sirs,

I configured RRAS with VPN + NAT on a Windows Server 2012:

Modem
192.168.25.1

Router
192.168.25.2 (WAN)
192.168.1.15 (LAN)

RRAS
192.168.1.244 (LAN / WAN)
172.16.0.1 (VPN)

I defined a static pool for VPN clients on range 172.16.0.1-172.16.0.100.
NAT is enabled on interface 192.168.1.244 (RRAS WAN).

I can:
- connect to the VPN;
- access/ping the server and internal network from VPN clients;
- access/ping the VPN client from the server.

I cannot:
- access/ping the VPN clients from machines on the internal network.

Does anyone have any ideas what could be causing this?
I'm at your disposal to provide any other required information.