Did you add it from the Channel Store? Or did you add it as a non-certified app?
Roku changed the non-certified app process. All previous ones went away, and the new ones are added as part of the newly-named Beta program. There is a limited time, and limited audience for non-certified apps.
Now, the developer of the app in question is, to my understanding, working to get the app certified in the Channel Store, but hasn't been successful to this point. But I understand he's working on it. Check the board. He's posted elsewhere about this.
Roku Community Streaming Expert
Note: I am not a Roku employee.
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