It all depends on your internet speed, so the first question is what speed do you get when running a speed test (both download & upload)? I have Spectrum (which is fast) & DA works fine for tablets, phones, computers, etc. at my home.
I am having the same issue, I could watch videos last week, but this week nothing is working.
Connection to the app requires an internet connected receiver with an internal Sling, like the Hopper 3 or Hopper with Sling. To provide the best experience there is a network bandwidth requirement of 800 Kbps or better for SD, 4 Mbps or better for HD. This connection is important to both the device you're viewing on and your DISH receiver at home.
If this is the case, can you log out of the app and uninstall it from the device and restart the device. Once restarted, can you go to the app store and reinstall the device.
Please take a look at an authentication issue that is mentioned in this thread. New version of Dish Anywhare constantly has problems with authenticating users. More importantly, it is a very poorly designed and managed service.