Dialup IPV6 address issue (IPSEC)

Hi, Have an IPSEC dialup (IPV6 over IPV4)  it was working fine until Oct 2018 was checking it before deployment this week not getting the ipv6 address now fortigate issues the ipv6 address ,  client is not picking and it is not a OS issue tried all options (Disabled OS firewall) ipv6 stack is enabled in the client PC.  Also couple of times it worked with IPV6, Same config file is working fine in a LAB setup it will be great to get some assistance Thank You AK