Similar problem here. Worked with the Dlink help chat yesterday and made a discovery. Found that live streaming of cameras located remotely in the app works when not on wifi (i.e. on cellular network). As soon as I switch to wifi locally, the app fails to stream the remote cameras. Web portal streaming is reliable on the same wifi, so clearly it is not a problem at the remote site. Looking at the remote router live bandwidth feed I can see the request for live streaming arrive from the app, then there is a steady flow of data out. No idea where the data goes...the app just fails with a "Connection Error". To add further confusion, I have two models of camera at the remote site (8600LH and an 8010LH), and sometimes the 8600 works (say, once in twenty attempts). The 8010 never works.
Have tried this with multiple mobile devices using different versions of OS (Android and Apple), ruling out the device.
Rebooted the cameras last time I was there. Same deal.
I have no idea what my local router might be doing to block the stream. Could it be blocking certain protocols, like say, UDP? I wonder if the RTSP traffic from these 8xxx series of cameras is sent over UDP. Anyone know? Grasping at straws here.