After certain period of time the ipv6 NS packets were not being being processes by the Debian server.
This caused the ipv6 NDP process to break but ipv4 works fine.
irb.xxx (MX/l2/l3) EVPN-MPLS ---et-x/x/x (ACX) |--- ethernet ---| enoxxx (HOST)
The IPv6 NDP process will be broken and no neighborship will be form
In this specific scenario the issue was pertaining to the NIC driver package on the Linux server.