When using the DJI Pocket 2 for RTMP at UHD it is not always compatable with RTMP servers.  The Pocket 2 is putting out a resolution of 1920 x 1088 instead of 1920 x 1080 which is causing the problem.  Of course it is more likely to fail with higher end RTMP servers which are somewhat picker about not getting set the resolution that they are expected to get.  

By contrast, 1920 x 1080 RTMP from the Action 2 and the DJI Fly app all work correctly.

DJI Pocket 2 RTMP at 720 and 460 work fine as the correct frame rates are sent with both these settings.

Hello there BobWinNV. Good day and thank you for posting these interesting information. Again, thank you for your valued support and keep filming.