Hi folks,
I did a wo update which updated to latest version of WordOps. I am not sure what version it was on before, but likely hadn't been updated for at least 6 months. The update when fine.
I then did a wo stack upgrade ... and it seemed to be going fine, but when I returned to the console (after leaving it for a few hours), it was hung on Stop : netdata [OK]. I assume it was hung, as I've never seen it take anything like 2+ hours for the stack upgrade before.
I hit CTRL-C a few times to break out of the script. This was the output:

natnut@nhnut:~$ wo stack upgrade
Nginx Stable is not already installed
Your sites may be down for few seconds if you are upgrading Nginx, PHP-FPM, MariaDB or Redis
Do you want to continue:[y/N]y
Updating APT cache              [OK]
Configuring php7.3-fpmes        [..]
Restarting php7.3-fpm           [OK]
Configuring php7.4-fpm
Restarting php7.4-fpm           [OK]
Tuning MySQL configuration      [OK]
Restarting mariadb              [OK]
Restarting fail2ban             [OK]
Configuring Fail2Ban
Restarting fail2ban             [OK]
Configuring APT Packages        [OK]
Downloading WP-CLI               [Done]
Downloading Netdata              [Done]
Downloading WordOps Dashboard    [Done]
Downloading PHPMyAdmin           [Done]
Downloading Adminer              [Done]
Downloading Adminer theme        [Done]
Downloading Composer             [Done]
Downloading MySQLTuner           [Done]
Downloading ngxblocker           [Done]
Stop  : netdata   [OK]
^CTraceback (most recent call last):
  File "/opt/wo/lib/python3.8/site-packages/wo/core/shellexec.py", line 24, in cmd_exec
    (cmd_stdout_bytes, cmd_stderr_bytes) = proc.communicate()
  File "/usr/lib/python3.8/subprocess.py", line 1028, in communicate
    stdout, stderr = self._communicate(input, endtime, timeout)
  File "/usr/lib/python3.8/subprocess.py", line 1868, in _communicate
    ready = selector.select(timeout)
  File "/usr/lib/python3.8/selectors.py", line 415, in select
    fd_event_list = self._selector.poll(timeout)
  File "/opt/wo/lib/python3.8/site-packages/cement/core/foundation.py", line 123, in cement_signal_handler
    raise exc.CaughtSignal(signum, frame)
cement.core.exc.CaughtSignal: Caught signal 2

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/bin/wo", line 8, in <module>
    sys.exit(main())
  File "/opt/wo/lib/python3.8/site-packages/wo/cli/main.py", line 102, in main
    app.run()
  File "/opt/wo/lib/python3.8/site-packages/cement/core/foundation.py", line 882, in run
    return_val = self.controller._dispatch()
  File "/opt/wo/lib/python3.8/site-packages/cement/core/controller.py", line 471, in _dispatch
    return func()
  File "/opt/wo/lib/python3.8/site-packages/cement/core/controller.py", line 471, in _dispatch
    return func()
  File "/opt/wo/lib/python3.8/site-packages/cement/core/controller.py", line 477, in _dispatch
    return func()
  File "/opt/wo/lib/python3.8/site-packages/wo/cli/plugins/stack_upgrade.py", line 389, in default
    WOShellExec.cmd_exec(
  File "/opt/wo/lib/python3.8/site-packages/wo/core/shellexec.py", line 38, in cmd_exec
    raise CommandExecutionError
wo.core.shellexec.CommandExecutionError

I tried running wo stack upgrade again, and it finished quickly (a minute or so), with all OK. As follows:

natnut@nhnut:~$ wo stack upgrade
[sudo] password for natnut:
Nginx Stable is not already installed
WordOps dashboard is not installed
Your sites may be down for few seconds if you are upgrading Nginx, PHP-FPM, MariaDB or Redis
Do you want to continue:[y/N]y
Updating APT cache              [OK]
Configuring php7.3-fpmes        [..]
Restarting php7.3-fpm           [OK]
Configuring php7.4-fpm
Restarting php7.4-fpm           [OK]
Tuning MySQL configuration      [OK]
Restarting mariadb              [OK]
Restarting fail2ban             [OK]
Configuring Fail2Ban
Restarting fail2ban             [OK]
Configuring APT Packages        [OK]
Downloading WP-CLI               [Done]
Downloading Netdata              [Done]
Downloading PHPMyAdmin           [Done]
Downloading Adminer              [Done]
Downloading Adminer theme        [Done]
Downloading Composer             [Done]
Downloading MySQLTuner           [Done]
Downloading ngxblocker           [Done]
Stop  : netdata   [OK]
Upgrading Netdata               [OK]
Upgrading Composer              [OK]
Upgrading phpMyAdmin            [OK]
Successfully updated packages

But the site has been down ever since.
I rebooted the server, and it's still down.

Where to from here?