If you use the option to open a console session from the Unraid GUI then you run commands just like on any other Linux system. Because Unraid is a cut-down Slackware based system then the command available may be limited to the more common (or Unraid specific) ones. The NerdTools plugin can be used to install additional commands.
That is an internal consistency check for a state condition that I do not expect to happen, but it should (in most cases) let things run without a problem. Was this error with the latest version of the plugin (2023.07.08) as if so I might give you instructions on how you could gather additional diagnostics to help identify the cause so I can correct for it.