Might as well capture my results here upgrading pfSense from 2.4.4p3 to 2.4.5...
SG-5100 - Primary Firewall - No issues with upgrade.
SG-2440 - Backup Firewall - On first boot after upgrade, no LAN or serial console access. Subsequent reboots no change. Ended up doing a memstick image install and then restoring configs from Primary. All good now.
Both systems use same trivial configuration and the packages are the same (apcupsd, arpwatch, sudo) except SG-2440 also has coreboot.
Peter