I had the same problem with my Galaxy S4 that I am having with my new Galaxy S6. Sometimes it works great, maybe for a month or two, then suddenly it will stop streaming music/video with slightly different characteristics. Currently, I can stream everything at my house with my home wifi. However, if I turn wifi off and use 4g, I can’t stream audio. The app still sees all my files, and will bring up the player page like its going to play, but never loads the file. The real odd thing is I can stream video currently on 4g or on public wifi, like a hotel wifi for example. I downloaded the MyCloud app onto my wife’s S6 and have the exact same problem. Once before, there was an update to the app and that seemed to fix it. Another time, I uninstalled/reinstalled the app, and that worked. Currently none of these solutions have worked. I have made no changes to my home network since this happened. The app stopped working while I was out of town. Any thoughts?
A thought: have you rebooted your router lately. Rebooting things periodically can do wonders sometimes.
I did and this actually seemed to work. I still have no idea why video would stream and audio would not. I wish the whole thing wasn’t as touchy as I have experienced.
All this wi-fi stuff is very strange, so once you accept that, understanding it gets easier!
Actually, I suppose the router lost track of an IP address, it happens frequently and why rebooting a router gets things straight again.