Hello,
I would like to share my experiences with the WD19TB and my Macbook Pro 15 2016 (4 Thunderbolt ports).
Since I've had three monitors for a while, I needed a dock because the connections were too few. For this reason I searched for a long time and at some point got stuck on the Dell D6000. So far, this has worked well except for the charging performance of my Macbook. Unfortunately, the D6000 only charges with a maximum of 60 watts, which often left my Battery empty over a hard day. It also got extremely hot and the "Display Link Monitor" software required extremely high resources.
So I searched further and came across the WD19TB, which according to forums and discussions on the net is not suitable for the Macbook and a triple monitor setup.
Nevertheless, I ordered the dock because I simply need at least 90W charging power.
Result: all three external screens (1x 4k 28 inch 60Hz, 1x WQHD 27 inch 120Hz, 1x 1080p 24 inch 60Hz) + the internal monitor of the Macbook work perfectly.
I plugged my 4k monitor into the display port connection on the dock, the 1080p via HDMI with an adapter (to USB C) into the Thunderbolt port on the dock. (where the cable goes to the notebook) I plugged the WQHD monitor directly into the Macbook via the display port on USB C so that I can use my 120Hz.
And now comes the important part!
You have to use the Thunderbolt port on the dock for one monitor. You can connect the other display to one of the other ports (HDMI or Display Port).
The Macbook Pro 15 has two Thunderbolt controllers. If you now connect the dock with the two monitors on one side and a monitor on the other side via the USB C port, you can use 3 monitors. I'm pretty sure this won't work on a 13 inch Macbook. But on a 16 inch it should.
Hope I could help a bit.