This can happen when the meeting room compute is connected to the Table Hub.  In this scenario, Rally is able to transmit from the Table hub to the Display Hub either one 4K signal or two 1080p streams.  

So, if a computer outputting a 4K signal is connected to the Table Hub, the second signal will not be transmitted - the 2nd screen will be black.  

Please configure the computer to do up to 1080p on the first screen before the second screen will display.

Note: In Windows, there are two locations where the display resolution needs to be checked or set. Please make sure the resolution is set to 1080p in both Display settings and Advanced Display Settings as follows:

1. Go to Settings and select System, then Display.
2. Make sure the resolution is set to 1920x1080.
3. Click on Advanced Display Settings.
4. Make sure the Active signal resolution is also set to 1920x1080.
5. If not, then click on Display adapter properties for Display.
6. Click on List All Modes and select an appropriate 1920x1080 mode that has a refresh frequency which is supported by your display. Most TVs support 60Hz when in 1080p mode, we recommend trying that first. If your TV doesn’t support 60Hz, try 30Hz and other options listed in the display settings menu.
7. The Active signal resolution should now show 1920x1080. 

Alternatively, in scenarios where access to computer settings is not desirable or possible, you can use an HDMI EDID emulator that limits the resolution to a maximum of 1080p/60Hz. The emulator should be placed in-line on HDMI 1 between the computer and the Table Hub. HDMI EDID emulators are widely available from multiple sources and in varying prices and capabilities.