iMac with Apple USB Ethernet won't boot after latest Security Update We have a number of iMacs (models 14,1 to 16,2) running in a StorNext 5 environment as Distributed LAN Clients (DLC).
These machines have Apple USB Ethernet adaptors attached to provide a secondary Ethernet interface for the StorNext Metadata network.
We have updated three machines (one 14,1 model, and two 16,2 models) with the most recent Security Update (not the latest 10.12.3 update).

All three machines fail to reboot until the Apple USB Ethernet adaptor is temporarily removed.
All three machines stay on a black screen indefinitely until the Apple USB Ethernet adaptor is removed.
Once the Apple USB Ethernet adaptor is unplugged the Apple logo appears and the machines boot up as normal.

This behaviour is consistent across all three machines since the update.
Machine #1 is a 14,1 model running El Capitan 10.11.6.
Machines #2 and #3 are 16,2 models running Sierra 10.12.2.
All three machines rebooted perfectly before the latest Security Update was installed.

Though we are able to re-insert the Apple USB Ethernet adaptor during boot time (and therefore get our SAN volume mounted) this is not an ideal situation.
All three of these machines are managed remotely, and if they are rebooted while unattended they will not come back online.

We have had some success making the USB Ethernet inactive in System Preferences/Network before applying the update, but this does not work every time.

TL;DR, the most recent Security Update for El Cap and Sierra breaks our iMacs with Apple USB Ethernet adaptors attached.

Anybody else encountered this?
It seems the latest update (10.12.3) for Sierra clients has fixed this problem, I was able to start one of the affected Macs from cold and restart without it sticking on the black screen.