After few hours of working under ~5000 sessions the system started to push the messages to monitor log
systemd-udevd[652354]: l2tp1683: Failed to get link config: No buffer space available
The systemd-udevd process got to 85+ Mb of memory and stopped growing further.
I saw some recommendations about systemd-udevd at accel-ppp forum but i can’t see the same files in vyos (version 1.4).