BUG: DHCPD 100% cpu when using failover IP
When using a redundant setup with a failover IP the CPU will go to 100% if the time on the two firewalls are different by a few minutes. When you bring the time back in sync the problem resolves itself.
If something goes wrong with your time synchronization this can occur. It also can occur if the time is off when first setting up the firewalls (before you configure NTP to sync the clocks).
Assuming it's dhcpd taking up 100% of the CPU, that would be an ISC DHCPD issue, not something we have anything to do with or any control over. If it's replicable I'd suggest reporting it to ISC.