I can connect the DJI Mimo app and the LightCut app from my phone to my Pocket 3 device, and I can control and record through the app.
But when I try to view playbacks that are on my device through either app, they just show as a black screen and I can not download them (it will show a download notification but stay at 0mb/s)

Has anyone run into this issue and is my device defective?

We apologize for the inconvenience. Due to the cellular network redirection policy in some countries or regions, the video may not be displayed or downloaded when previewing due to a network conflict. When this error appears while previewing, please turn off the mobile phone’s mobile network. Then, launch DJI Mimo for previewing or downloading.

Try changing your recording format to H264 you may find that is more compatible.  

I have the same issue.  Did any of the advice help you?  I don't know how to turn off my iphones mobile network and not sure that is a good idea.