Thank you so much for reaching out to us, I am sorry to hear that you are running into this issue, but I would be more than happy to assist!
This has been something that we have attempted to follow very closely, as we have seen varied behavior with the 4K “Alt Mode” output. Some customers have reported no issues, others have not been able to get the output to work.We do not recommended it if 4K “Alt Mode” output is required. There is even a 24 page thread on Lenovo’s site regarding Alt Mode challenges on the Yoga 920 located here -> https://goo.gl/jMK5h
Just to make sure this problem is related to what you are experiencing, I want to see if the log files from your system give us some additional information. When you have a moment, could you please keep everything connected and send us the output of our diagnostic utility PlugDebug --> http://plugable.com/support/plugdebug as this will allow us to examine some log files from your system to help determine the next steps.
Once the application completes, a .zip file should be located on your desktop. Please attach this .zip file to a direct email, and send it to firstname.lastname@example.org. Please put “Ticket no. 232970” into the subject line so we can keep all of your information in the same place.
Thank you for your time,
Product Owner & Technical Support