You didnt mention your Roku model # or firmware version (Settings/System/About) or app name/version (highlight the app and press Options (*) on the remote).
You are using the term "download" - do you mean stream?
You also haven't described any error messages or specific behavior.
Considering the same general behavior occurs on very different platforms that suggests:
1) Bandwidth constraint issue with your network/internet connection - maybe
2) App bug - least likely
3) NFL streaming server issue - most likely
You should verify your network streaming stability/speed (perhaps other apps), then contact the NFL:
https://www.nflgamepass.com/en/contact-us
