19.7.3: Reconnecting PPPoE does not remove old IPv6 addresses from interface

[schnipp]

In case the PPPoE connection drops (e.g. lost DSL sync, ppp termination, ...) the connection is triggered again by the mpd daemon. After the connection is established, the ISP assigns a fresh ipv4 address and IPv6 prefix to generate a new IPv6 host address for the firewall (SLACC based). Additionally, Opnsense assigns a temporary SLAAC address with privacy extensions enabled.

But, after retriggering PPPoE and getting a new IPv6 prefix the IPv6 addresses based on the outdated prefix won't be deleted from the interface. So, there is no chance that services using the old addresses can communicate with the internet (e.g. unbound DNS).