Please edit the file /etc/systemd/system/multi-user.target.wants/syslog-ng.service.
Under the [Service] section, add:
LimitMEMLOCK=XXXXXXXXX
Where XXXXXXXXX is replaced with the appropriate amount of memory needed for the udp-balancer() to run effectively.
268435456 is the minimum recommended memory allocation (256mb).
Then save and exit the file, and run
# systemctl daemon-reload
# systemctl restart syslog-ng
If Syslog-ng PE still fails with the same error, please increase the memory further and try again.