Try removing the channel from the Roku home screen by navigating to the channel tile, pressing the * key on your remote and choosing 'Remove channel'. Then restart your device from Settings>System>System restart. Once your player starts up again, add the channel back once more.
Does this clear up the issue you are seeing? Please keep us posted.
I tried removing and reinstalling the app. No change. I did see in this forum on other issues that the recommendation was to disable the "Airtime Fairness" in the wireless section of home routers.
I disabled it on my router and that has fixed the problem.
Interestingly in addition to allowing the login to the app taking place it also stopped the network errors I was getting when this app was trying to load its content of what tennis matches were available to watch.