Comment migrated from old forum on 9/14/2018. Original post by Plugable Support, Bob:
Hello and thanks for posting!
Thank you as well for the detail you provided and the testing you have already performed that is much appreciated.
In short, the behavior you are seeing is due to an internal design choice made by Asus and unfortunately cannot be changed.
To expand further, manufacturers have substantial discretion when designing their systems as to how many displays are supported via a single Thunderbolt 3 connection. Some manufacturers, such as Apple and Dell, support two displays via a single Thunderbolt 3 connection, while systems from other manufacturers often can only support one display. This is a result of how many DisplayPort video lanes have been routed internally to the system’s Thunderbolt 3 port.
We do our best to call out this potential behavior in our product listings on Amazon and in our compatibility table on our own product page -> https://plugable.com/products/tbt3-ud… We have had customer reports that Asus ROG systems only support one display via Thunderbolt 3 (noted in our compatibility table), and your results confirm that your system in fact only supports one display via a single Thunderbolt 3 port.
The workaround in your case would be to connect one display to the docking station, and one display to the HDMI output built-in to the laptop. If that workaround is not acceptable, even though the source of the problem is outside of our control we do offer a 30-day no-hassle return policy for all products sold by Plugable and fulfilled by Amazon.
If you would prefer to return the unit, please send your Amazon Order ID number to us directly via email@example.com with ‘For ticket #234801’ in the subject line so we can match everything up and get the return process started (please do not post this information in our public forum).