I have struggled with this issue for some time now and have just recently thought I would fight the fight again. When I originally purchased the M1 I wanted to be able to watch TV in other parts of the house without running cables. I had an iPad and AppleTV and could never get it to work. The stream would be looking good and all of a sudden the quality would start ramping down and then finally it would drop the connection. Fast forward a year or so and now I can download the app on my Amazon Fire. Same problem and it doesn't matter if I'm wired or wireless. I'm running an Asus RT-N66U and UPnP is enabled with port forwarding, etc.
Suggestions? I have to believe it's some type of configuration issue, but I really can't find anything wrong with the settings - and it shouldn't be this difficult to get this running. I haven't had a chance to test this away from the network, but last year I was able to run the app on the iPad away from home with minimal issues.