On each ppp interface creation, we can see excess call to isis (isis is not configured), and udev
Jan 23 19:10:00 R2-QAT systemd-udevd[31716]: link_config: autonegotiation is unset or enabled, the speed and duplex are not writable. Jan 23 19:10:00 R2-QAT isisd[1719]: circuit already disconnected
It makes pretty overhead on high load PPPoE BRAS on client's mass authentication.
It will be good to fix this moment.
Proposition:
Run isis only if it configured as we do it with PIM/IGMP (pimd daemon)
Exclude udev call for ppp interfaces