Please turn the Matrix on before turning on external AES devices to prevent this issue.
Some users have reported no signal over the AES output.
In circumstances where measurements were able to be taken, typically the level reads around -138 dBFS and changing levels on the console makes no difference.
This has been replicated by SSL, and is due to instances of back-power being fed into the AES inputs from some external hardware during the boot-up sequence of Matrix, which causes the AES outputs to fail.
To prevent this issue, turn AES devices on after the Matrix has booted.