Softwareupdate command not working via Terminal.

While ssh'd into a client with no user logged in via the GUI.

After running:

bash-3.2# softwareupdate -l
Software Update Tool

Finding available software
Software Update found the following new or updated software:
* Label : macOS Big Sur 11.5.1-20G80
        Title: macOS Big Sur 11.5.1, Version: 11.5.1, Size: 2859335K, Recommended: YES, Action: restart,

The update is detected successfully as expected.

After running:

bash-3.2# softwareupdate -da
Software Update Tool

Finding available software 
Downloading macOS Big Sur 11.5.1
Downloading: 100.00%
Donwloaded: macOS Big Sur 11.5.1

The update is downloaded as expected.

After running:

bash-3.2# softwareupdate -iaR
Software Update Tool

Finding available software
Downloading macOS Big Sur 11.5.1

Downloaded: macOS Big Sur 11.5.1
Restarting...
bash-3.2#

It appears to do the installation and restart but after returning to the bash prompt the computer never restarts. In the past this worked, what changed?

However, if a user is logged in via the GUI the command will work.

This is backwards, I would expect the command to NOT work while a user is logged in.