I have been using Emby for a couple of years now, and over the last couple of days my FireTv apps will sit with a spinning circle when opened.  They only way to get the apps to work is to go into the FireTV settings and clear the app data.  Once cleared, the app connects almost instantly and works fine until the next day or a couple hours after use.  I have a Samsung TV with the app, and the issue does not show on it.