Thanks for getting back, appreciate the confirmation and apologies for my misunderstanding.
I replicated the behavior you are seeing in house, and the short version is that this appears to be a combination of the Windows bug I mentioned previously and an application specific issue with the GoPro app. A workaround that worked in my test setup was to import and convert the clip(s) while using the ‘View & Trim’ tab when the GoPro application window was located on the internal laptop display. Once converted and then by switching to the ‘Edit’ tab of the application, the video played as expected when the application window was then moved back to a display connected to the dock.
If you will pardon the technical digression, the long version is that with the release of the Windows Anniversary Update (that your system is now running) Microsoft has made low-level graphics changes that can cause applications that require the use of OpenGL (which the GoPro app requires -> https://shop.gopro.com/softwareandapp… under the ‘System Requirements’ tab) not to work as expected.
To expand further, the operating system incorrectly routes OpenGL tasks meant for the for the internal graphics adapter in your system to the wrong place causing certain functions not to work. In instances where this has affected those using our products, the two methods I suggested previously (changing the ‘Main’ display or plugging in our product after the application launch) have been able to workaround this Microsoft bug and yours is the first such report we have had to the contrary.
I replicated the behavior you are seeing with one of our test systems and the UD-3900 dock, but where it got interesting (and confirms the source of the behavior is within Windows and the app itself) is when I was I able to get it to happen when no Plugable products where in use.
The laptop I tested with has two internal graphics adapters, one from Intel and one from Nvidia, in what is known as a hybrid graphics setup. Utilities from the graphics adapter manufacturer allow you to change which adapter is in use, and when I explicitly switched from the Intel adapter to the Nvidia adapter, I again replicated the same behavior you describe. The video image in the playback window while using the ‘View and Trim’ tab was blank/black, but would ‘play’ in that the time indicator would increment and I could hear the audio. Again, this was with no Plugable products in use/connected.
Searching the GoPro support forums for similar behavior turned up a few results (none using our products though) which led me to the workaround I mentioned above. While I can’t be 100% certain, the GoPro application appears to be using a different method to display the video between the two ‘View & Trim’ and ‘Edit’ tabs, accounting for the difference in behavior.
Summing up, the initial cause of the change in behavior was most likely your system updating to the Anniversary Update exposing both the Windows bug and the GoPro specific application issue. Microsoft will have to address the issue in a future update to Windows 10 and/or GoPro would have to update their application to fix the root cause, but in the interim the workaround I suggested above appears to be the only solution.
Apologies for the very long response…please let me know if the workaround I described works on your system or if you have any additional questions, and thank you again for your patience!