all files under `/var/run/` (a symbolic link to `/run`) must be created from scratch on server reboot. Could you make a test: 1) systemctl disable kamailio 2) reboot 3) ls -ld /var/run/kamailio 4) ls -l /var/run/kamailio 5) systemctl enable --now kamailio 6) ls -ld /var/run/kamailio 7) ls -l /var/run/kamailio
And paste here output of these commands.