App acting differently on 2 different devices

I have a streaming app which has an internal player (not great) but it also allows us to use MX Player. The app is installed on my Android TV and also my Nvidia shield. On the android TV, if I chose to use the External player (MX Player) it works fine, MX player comes up and the stream plays there fine. On the shield, when I select to play on the External player, It opens the Play Store and a message pops up on the bottom of the screen asking me to install MX Player. However, MX player is already installed. I have tried uninstalling and reinstalling but it makes no difference. It is the exact same app on both devices and I can not understand why it works perfect on one but not the other. Are there any recommended areas to check?