Re: Dell Precision 5530 i9 + WD19TBdock + 2 Displayports = screen flickering

Another user reported different display-related issues with the WD19TB in this thread.  Basically, after a while the user found that dual 4K was possible but sometimes one display will only come up at 1080p.  Just to confirm, did you update the firmware specifically for the Thunderbolt controller in your system?  I see that you updated the laptop firmware and the Thunderbolt drivers, but there's a separate Thunderbolt controller firmware update.  The direct link to the latest version as of this writing is here.

If you've done that and are still having this issue, then my guess as to what's going on is the same as my guess for what's going on in that other thread: issues with the initial firmware release of a brand new WD19TB.  Unfortunately initial release bugs are pretty much an industry-wide thing these days.  A Dell rep in that other thread said that a WD19TB firmware update was slated for August but didn't know the exact details of the changes.