Problem Solved.
The issue was that the F5 had previously been configured with ntp servers.
tmsh modify /sys ntp servers replace-all-with { 192.168.2.5 }
When the /etc/ntp.conf file was reviewed, we found the following entries:
server 192.168.2.5 iburst
and, because of following SOL14120:
server 192.168.2.5 key 1 iburst
The NTPD grabbed and used the first such entry, which was NOT using a key for authentication. As such, the F5 unit was continually attempting to communicate to the ntp server without using authentication.
Solution: "tmsh modify /sys ntp servers none"
followed by "tmsh save /sys config partitions all"