When the display goes into sleep mode, a user connecting to that macOS gets a black screen.

During tests in our labs we noticed that if the macOS is not configured to 'Prevent computer from sleeping automatically when the display is off', user gets a frozen desktop or 'No available sessions'.

As a workaround, prevent the macOS from turning the display off by setting 'Turn display off after: Never' in System Preferences > Energy saver.