Please take a look at this flow chart. The clock is controlled by the navigation unit and it sends a signal to the audio unit which sends the signal to the Sub-display.
Unfortunately, there is no easy way to diagnose this but I suspect you have an issue in the Audio/HVAC display module. Each of the two items are inputs to this unit and it just appears to be the only common denominator.
This is a chance that you have two issues but it is unlikely but it would still be a good idea to have it checked out just to be sure because this is not a cheap part that we want to get wrong.
Please let me know if you need more information. Thanks
Images (Click to enlarge)
Saturday, June 29th, 2019 AT 3:49 PM