Does it reconnect as expected using the old mpd5/netgraph?
Is it failing at both IPv4 and IPv6?
If you disable IPv6 does it then reconnect correctly?
We have seen one other report from an A&A user but that failed to connect after reboot.
https://forum.netgate.com/topic/198027/if_pppoe-problems-with-php-fpm-causing-loops-resolved