Monitoring IPv6 WAN logs

[pbnet]

Hello,

I have native IPv6 from my ISP assigned though PPPoE with Prefix Delegation (they assign a /64).
This week the ISP upgraded the firmware on the ONT providing the connection and so far I encounter the following issue:

• PFSense WAN interface periodically loses its IPv6 IP.
  First I suspected a port flap or something, but the uptime of the interface is in the range of days.

Is there a way I can find in PFSense logs when the interface lost its IPv6 address ?

Thanks a lot,
Andy