What model / year is your Shield?
I have a 2015 and a 2017 Shield and Optus Sports works on both.
Have you tried to clear data / clear cache / reinstall?
Does the Kodi add-on work for you (not saying you should use it, but just as a test)?
You might have more luck troubleshooting / getting advice over on the Shield and Optus Sports threads on Whirlpool:
I bought a Hisence Android TV RG55 to watch optus sport. I downloaded the app from the app store and opened , it said 'This application is not supported on rooted devices'. I have not set or installed anything since it is taken out of the box. Why would this message appear and how can I fix that and watch it on my TV? Cheers
Is anybody else having issues with the Optus Sport Android TV app since the COVID-19 break?
I can no longer use the enter/select button on my remote to select videos.
I can navigate around the screen (up/down/left/right) I just can't select.
My select button works on all other apps.
I'm using an Nvidia Shield TV Pro 2017.